send21-io

aid: send21-io
name: send21-io
image: https://send21.io/og/send21-card.png
description: Send21 provides a non-custodial crypto payment link service and API for people and AI agents. Users can create
  pay links or invoices priced in various cryptocurrencies, including BTC, USDC, USDT, EURC, SOL, and ETH, and pay directly
  from their wallets via on-chain or Lightning. The platform emphasizes security, stating that it never holds users' money
  or private keys, and offers documentation, pricing, and demo pages for developers and businesses.
url: https://artifacts.apis.io/send21-io/apis.yml
x-type: company
x-source: harvest:mcp-registry
x-tier: profiled
x-tier-reason: enrichment pass 2026-10-31 (modular-v1; was harvest)
specificationVersion: '0.20'
created: '2026-10-31'
modified: '2026-10-31'
tags:
- Company
- Payments
- Crypto
- API
- Non-custodial
- AI
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: AgenticAccess
  url: agentic-access/send21-io-agentic-access.yml
- type: Plans
  url: plans/send21-io-plans-pricing.yml
- type: Spectral
  url: rules/send21-io-rules.yml
- type: JSONLD
  url: json-ld/send21-io-context.jsonld
- type: Vocabulary
  url: vocabulary/send21-io-vocabulary.yml
- type: Webhooks
  url: asyncapi/send21-io-webhooks.yml
- type: DataModel
  url: data-model/send21-io-data-model.yml
- type: Idempotency
  url: conventions/send21-io-conventions.yml
- type: Conventions
  url: conventions/send21-io-conventions.yml
- type: Security
  url: security/send21-io-vulnerability-disclosure.yml
- type: Authentication
  url: authentication/send21-io-authentication.yml
- type: ErrorCatalog
  url: errors/send21-io-problem-types.yml
- type: Conformance
  url: conformance/send21-io-conformance.yml
- type: LLMsTxt
  url: llms/send21-io-llms.txt
- type: SecurityTxt
  url: well-known/send21-io-security.txt
- type: WellKnown
  url: well-known/send21-io-well-known.yml
- type: Hosts
  url: hosts/send21-io-hosts.yml
- type: Vendors
  url: vendors/send21-io-vendors.yml
- type: Login
  url: https://send21.io/login
- type: VulnerabilityDisclosure
  url: security/send21-io-vulnerability-disclosure.yml
- type: DomainSecurity
  url: security/send21-io-domain-security.yml
- type: Website
  url: https://send21.io/
- type: Documentation
  url: https://send21.io/docs
- type: APIReference
  url: https://send21.io/swagger/v1/swagger.json
- type: GettingStarted
  url: https://send21.io/docs/quickstart
- type: Support
  url: https://send21.io/about
- type: GitHubOrganization
  url: https://github.com/send21io
- type: Pricing
  url: https://send21.io/pricing
- type: TermsOfService
  url: https://send21.io/terms
- type: PrivacyPolicy
  url: https://send21.io/privacy
apis:
- aid: send21-io:send21-io-account-api
  name: send21-io Account API
  description: The Account API from send21-io — 2 operation(s) for account.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Account
  properties:
  - type: OpenAPI
    url: openapi/send21-io-account-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-auth-api
  name: send21-io Auth API
  description: The Auth API from send21-io — 26 operation(s) for auth.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Auth
  properties:
  - type: OpenAPI
    url: openapi/send21-io-auth-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-checkout-api
  name: send21-io Checkout API
  description: The Checkout API from send21-io — 3 operation(s) for checkout.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Checkout
  properties:
  - type: OpenAPI
    url: openapi/send21-io-checkout-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-demo-api
  name: send21-io Demo API
  description: The Demo API from send21-io — 3 operation(s) for demo.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Demo
  properties:
  - type: OpenAPI
    url: openapi/send21-io-demo-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-drafts-api
  name: send21-io Drafts API
  description: The Drafts API from send21-io — 13 operation(s) for drafts.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Drafts
  properties:
  - type: OpenAPI
    url: openapi/send21-io-drafts-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-fees-api
  name: send21-io Fees API
  description: The Fees API from send21-io — 3 operation(s) for fees.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Fees
  properties:
  - type: OpenAPI
    url: openapi/send21-io-fees-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-rates-api
  name: send21-io Rates API
  description: The Rates API from send21-io — 1 operation(s) for rates.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Rates
  properties:
  - type: OpenAPI
    url: openapi/send21-io-rates-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-recurringtemplates-api
  name: send21-io Recurring Templates API
  description: The RecurringTemplates API from send21-io — 4 operation(s) for recurringtemplates.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - RecurringTemplates
  properties:
  - type: OpenAPI
    url: openapi/send21-io-recurringtemplates-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-suggestions-api
  name: send21-io Suggestions API
  description: The Suggestions API from send21-io — 1 operation(s) for suggestions.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Suggestions
  properties:
  - type: OpenAPI
    url: openapi/send21-io-suggestions-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-webhooks-api
  name: send21-io Webhooks API
  description: "**send21 calls your server when a draft changes.** Register an endpoint with `POST /api/v1/webhooks`\n(scope\
    \ `webhooks:manage`) and pick the events you want. The response contains the signing secret\nonce; store it. Send a signed\
    \ test event any time with `POST /api/v1/webhooks/{id}/test`.\n\n### Delivery\n\nA `POST` to your URL with `Content-Type:\
    \ application/json` and this body:\n\n```json\n{ \"event\": \"draft.confirmed\", \"data\": { ... } }\n```\n\n| Header\
    \ | Meaning |\n|---|---|\n| `X-Send21-Event` | The event type, same as `event` in the body. |\n| `X-Send21-Delivery` |\
    \ Unique delivery id. Retries reuse it, so use it to ignore duplicates. |\n| `X-Send21-Signature-V2` | `t=<timestamp>,v1=<hex\
    \ HMAC-SHA256 of \"<timestamp>.<delivery id>.<raw body>\">`, keyed with your secret. Verify this one: it also signs the\
    \ time and the delivery id, so a copied delivery cannot be replayed later. Refuse deliveries older than 5 minutes (300\
    \ seconds). |\n| `X-Send21-Timestamp` | When the delivery was sent, in Unix seconds (the same value as `t=`). |\n| `X-Send21-Signature`\
    \ | Original signature, kept for existing integrations: `sha256=` followed by the lowercase hex HMAC-SHA256 of the raw\
    \ body only. It has no timestamp, so a copied delivery passes it again. |\n\nAny 2xx response counts as delivered. Anything\
    \ else, or no answer within 15 seconds, is retried\nafter 1, 2, 4, 8 minutes and so on, up to 8 attempts. Deliveries can\
    \ arrive out of order.\n\n### Verifying the signature\n\nCheck `X-Send21-Signature-V2`: compute the HMAC over `<timestamp>.<delivery\
    \ id>.<raw body>`, using the\nraw request bytes before parsing the JSON, compare in constant time, and refuse deliveries\
    \ more than\n300 seconds old. Answer 401 when the header is missing or wrong. The same check as on\nsend21.io/docs/webhooks:\n\
    \n```js\n// X-Send21-Signature-V2: t=<unix seconds>,v1=<hex HMAC-SHA256 of \"<t>.<delivery id>.<raw body>\">\nconst sig\
    \ = String(req.headers['x-send21-signature-v2'] ?? '');\nconst t = /(?:^|,)t=(\\d+)/.exec(sig)?.[1];\nconst v1 = /(?:^|,)v1=([0-9a-f]{64})/.exec(sig)?.[1];\n\
    const deliveryId = String(req.headers['x-send21-delivery'] ?? '');\nconst fresh = t !== undefined && Math.abs(Date.now()\
    \ / 1000 - Number(t)) <= 300;\nconst expected = crypto.createHmac('sha256', secret)\n  .update(t + '.' + deliveryId +\
    \ '.').update(rawBody).digest('hex');\nconst ok = fresh && v1 !== undefined &&\n  crypto.timingSafeEqual(Buffer.from(v1,\
    \ 'hex'), Buffer.from(expected, 'hex'));\nif (!ok) return res.status(401).end();\n```\n\nBefore you ship goods, check\
    \ that the confirmed amount, currency and `orderId` are the ones you\nexpect, or fetch `GET /api/v1/drafts/{id}` with\
    \ your API key and check its status there.\n\n### Events\n\n| Event | When |\n|---|---|\n| `draft.created` | A draft was\
    \ created: by you, an API key, a recurring template, or a payer picking a currency on a pay link. |\n| `draft.seen` |\
    \ A payment for the draft was seen, but is not confirmed yet. Also sent when you accept a payment with a different amount\
    \ (`acceptedByOwner: true`); `draft.confirmed` follows once that transfer has the required confirmations. |\n| `draft.confirmed`\
    \ | The payment reached the required confirmations. For Lightning: the provider confirmed it with a valid preimage. |\n\
    | `draft.amount_mismatch` | A transfer needs your decision (`reviewState: pending`). `reviewReason: \"amount\"`: it arrived\
    \ within 10% of the billed amount, but not the exact amount. `reviewReason: \"rate_lock_expired\"`: a pay-link payment\
    \ of the exact amount arrived more than 10 minutes after its rate lock ended, so it was priced at an older rate. It does\
    \ not pay the draft until you accept it with `POST /api/v1/drafts/{id}/accept-received`; decline it with `POST /api/v1/drafts/{id}/reject-received`.\
    \ Sent once. |\n| `draft.mismatch_accepted` | A payment with a different amount was accepted, by you (`acceptReason`)\
    \ or by the draft's `shortfallPolicy` (`acceptReason: \"auto: shortfallPolicy\"`). Carries `expectedAmountSats`, `receivedAmountSats`,\
    \ `acceptedBy` and `acceptedAt`. |\n| `draft.mismatch_rejected` | You declined it (`rejectReason`, `rejectedBy`, `rejectedAt`).\
    \ `refund: \"manual\"`: the money is in your wallet and send21 cannot return it. |\n| `draft.mismatch_reminder` | Still\
    \ undecided 2 hours before the draft expires. Sent once. |\n| `draft.mismatch_unresolved` | The draft expired or was cancelled\
    \ while the transfer was undecided. The money arrived and is in your wallet; you can still accept it. |\n| `draft.expired`\
    \ | The draft expired unpaid. If an undecided transfer with a different amount arrived, `receivedAmountSats` is set and\
    \ `reviewState` is `unresolved`. Pay-link payments also carry `opened`, `quoteRequested`, `firstOpenedAt` and `quoteRequestedAt`.\
    \ |\n| `draft.cancelled` | The draft was cancelled. |\n| `payment_request.expired` | A pay link expired unpaid. `opened`:\
    \ the payer loaded the pay page (link previews and bots ignored). `quoteRequested`: they picked a currency. `reviewState`\
    \ if a differing transfer arrived. No IP or payer data. |\n| `test` | Sent by the test endpoint. `data` has `message`\
    \ and `occurredAt`. |\n\n### Payload of draft.seen, draft.confirmed, draft.amount_mismatch and draft.expired\n\nAmounts\
    \ ending in `Sats` are base units of the sent asset: 8 decimals for BTC, 6 for USDC, USDT and\nEURC, 9 for SOL and ETH\
    \ (ETH amounts are in gwei). `txId` is the transaction id or signature; for Lightning it is the payment hash. For native\
    \ ETH\nfound by the balance fallback from a smart-wallet transfer, it is `block-<number>`.\n`receivedAmountSats` and `receivedAmount`\
    \ are set only when the amount differs from the billed amount,\nincluding on the `draft.confirmed` of an accepted short\
    \ or over payment, so you can record what arrived.\n`paymentRequestId` and `orderId` are set for pay-link payments.\n\n\
    ```json\n{\n  \"event\": \"draft.amount_mismatch\",\n  \"data\": {\n    \"draftId\": \"3f6c2a9e-5d1b-4c8e-9a7f-2b4d6e8f0a1c\"\
    ,\n    \"status\": \"AwaitingPayment\",\n    \"txId\": \"5KqZ9bQ...\",\n    \"confirmations\": 1,\n    \"receivedAmountSats\"\
    : 49250000,\n    \"receivedAmount\": \"49.250000\",\n    \"sentCurrency\": \"USDC\",\n    \"network\": \"Solana\",\n \
    \   \"amountSats\": 50000000,\n    \"sentAmount\": \"50.000000\",\n    \"fiatCurrency\": \"EUR\",\n    \"fiatAmount\"\
    : 46.00,\n    \"conversionRate\": 0.92,\n    \"rateSource\": \"coinbase\",\n    \"platformFee\": {\n      \"accrued\"\
    : true, \"waived\": false, \"percent\": 0.39, \"feeUsd\": 0.20,\n      \"feeBaseUnits\": 195000, \"feeAmount\": \"0.195000\"\
    , \"currency\": \"USDC\"\n    },\n    \"paymentRequestId\": \"8d1e4b7a-0c2f-4e6d-b3a9-7f5c1e2d4a6b\",\n    \"orderId\"\
    : \"ORDER-1042\",\n    \"occurredAt\": \"2026-10-06T08:22:22Z\"\n  }\n}\n```\n\n### Payload of draft.created and draft.cancelled\n\
    \n`draft.created` has `draftId`, `amountSats`, `network` and `occurredAt`; pay-link drafts add\n`paymentRequestId`, `orderId`\
    \ and `currency`. `draft.cancelled` has `draftId`, `status`, `network`,\n`amountSats`, `paymentRequestId` and `occurredAt`."
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Webhooks
  properties:
  - type: OpenAPI
    url: openapi/send21-io-webhooks-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-address-book-api
  name: send21-io Address Book API
  description: The Address Book API from send21-io — 2 operation(s) for address book.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Address Book
  properties:
  - type: OpenAPI
    url: openapi/send21-io-address-book-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-api-keys-api
  name: send21-io API Keys API
  description: The API Keys API from send21-io — 2 operation(s) for api keys.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - API Keys
  properties:
  - type: OpenAPI
    url: openapi/send21-io-api-keys-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
- aid: send21-io:send21-io-payment-requests-api
  name: send21-io Payment Requests API
  description: The Payment Requests API from send21-io — 3 operation(s) for payment requests.
  humanURL: https://send21.io/docs
  baseURL: https://send21.io
  tags:
  - Payment Requests
  properties:
  - type: OpenAPI
    url: openapi/send21-io-payment-requests-api-openapi.yml
  - type: JSONSchema
    url: json-schema/send21-io-draft-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-payment-request-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-quote-info-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-create-draft-request-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-fee-breakdown-response-schema.json
  - type: JSONSchema
    url: json-schema/send21-io-demo-draft-response-schema.json
x-enrichment:
  date: '2026-10-31'
  status: enriched
  artifacts_added: 30
  pass: modular-v1
  engine: identity=local,contract=local,surfaces=local,docs=local,regulatory=local