# Stax

**Canonical:** https://apis.io/providers/stax/  
**Website:** https://staxpayments.com/  
**APIs profiled:** 1

Stax (formerly Fattmerchant) is an Orlando, Florida payments technology company that sells subscription-priced payment processing to small and large merchants (Stax Pay), embedded payments and merchant onboarding to SaaS platforms and ISVs (Stax Connect), compliant credit-card surcharging (CardX by Stax), automated subscription billing (Stax Bill), and full-stack processing for partners and ISOs (Stax Processing). Its public REST API at apiprod.fattlabs.com covers charges, credits, refunds and voids, stored payment methods and tokenization, customers, invoices and invoice schedules, payment links, catalog items, terminals and card-present devices, merchant enrollment and underwriting, disputes, statements and deposit reporting, teams, users and API keys, and merchant- and partner-level webhooks. Stax.js handles browser tokenization; iOS and Android SDKs cover card-present and Tap to Pay. Stax Payments, Inc. is a registered ISO/MSP of Fifth Third Bank and Synovus Bank and a registered partner/ISO of Elavon, Inc.

## Kin Score — 74.8 / 100 (exemplar)

Scored 2026-09-01 under rubric 0.17.2. Trend: flat (+0.0 from 74.8).

| Facet | Score |
|---|---|
| Discoverability | 75.9 |
| Contract Quality | 57.8 |
| Governance | 18.2 |
| Contract Governance | 18.2 |
| Operational Transparency | 84.2 |
| Developer Ergonomics | 78.6 |
| Commercial Clarity | 92.1 |
| Access Clarity | 92.1 |

Regulatory layer — **Payments**: 68.8 (matched via tags).

## Agent readiness — 50.9 (agent-native)

| Dimension | Value |
|---|---|
| Spec Presence | yes |
| Agentic Access | yes |
| Reversibility Documented | no |
| MCP Server | documented |
| Auth Clarity | bearer |
| Idempotency | verified |
| Error Semantics | documented |
| OpenAPI Examples | verified |
| Rate Limit Signal | documented |
| Event Surface Described | yes |
| Agent Skills | yes |
| Well Known Catalog | no |
| Consent Identity | no |
| Agent Card | no |
| Dry Run Mode | no |
| Delegated Identity | no |
| Protected Resource Metadata | no |
| Dynamic Client Registration | no |
| Agentic Commerce | no |

## APIs (1)

- **Stax API** — The Stax REST API (published as "stax-api") exposes 133 operations across 101 paths at https://apiprod.fattlabs.com — the Merchant API for payments, payment methods, customers, ...

## MCP servers (1)

- **Stax Docs MCP Server** — Stax hosts a remote MCP server at https://docs.staxpayments.com/mcp. It answered an anonymous initialize + tools/list on 2026-08-29 (protocolVersion 2025-06-18, serverInfo {name...

## Agentic access (1)

- **Stax Agentic Access** — 133 operations · 79 acting · 2 human-in-the-loop

## Security (4)

- **Stax Authentication** — http · 3 schemes
- **Stax Domain Security** — TLSv1.3 · DMARC
- **Stax Vulnerability Disclosure** — Hackerone · security.txt · contact published
- **Stax Trust Center** — trust center published

## Plans (1)

- **Stax Plans Pricing**

## Tags

Payments, Payment Processing, Merchant Services, Embedded Payments, ACH, Invoicing, Subscription Billing, Surcharging, Point-of-Sale, Tokenization, Financial-Services, Fintech, Card Present, Merchant Onboarding

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Profiled by [API Evangelist](https://apievangelist.com) and published on [APIs.io](https://apis.io/providers/stax/). Scores are computed from the provider's own public artifacts under a published rubric.