WHMCS Billing API

openapi: 3.0.3
info:
  title: WHMCS Authentication Billing API
  description: The WHMCS API provides an interface to perform operations and actions within WHMCS from external applications and scripts. It supports client management, billing, orders, domain management, support tickets, and system administration.
  version: 1.0.0
  contact:
    name: WHMCS Developer Documentation
    url: https://developers.whmcs.com/api/
  license:
    name: WHMCS License
    url: https://www.whmcs.com/license/
servers:
- url: https://{your-domain}/includes/api.php
  description: WHMCS API endpoint (self-hosted installation)
  variables:
    your-domain:
      default: example.com
      description: Your WHMCS installation domain
security:
- ApiCredentials: []
tags:
- name: Billing
  description: Invoice, payment, and transaction management
paths:
  /?action=GetInvoices:
    post:
      operationId: getInvoices
      summary: Get Invoices
      description: Retrieve a list of invoices from WHMCS.
      tags:
      - Billing
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              allOf:
              - $ref: '#/components/schemas/AuthCredentials'
              - type: object
                properties:
                  limitstart:
                    type: integer
                  limitnum:
                    type: integer
                  userid:
                    type: integer
                    description: Filter by client user ID.
                  status:
                    type: string
                    description: Invoice status filter.
                    enum:
                    - Unpaid
                    - Paid
                    - Cancelled
                    - Refunded
                    - Collections
                    - Draft
      responses:
        '200':
          description: List of invoices.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/InvoicesListResponse'
  /?action=GetInvoice:
    post:
      operationId: getInvoice
      summary: Get Invoice
      description: Retrieve a specific invoice from WHMCS.
      tags:
      - Billing
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              allOf:
              - $ref: '#/components/schemas/AuthCredentials'
              - type: object
                required:
                - invoiceid
                properties:
                  invoiceid:
                    type: integer
                    description: The ID of the invoice to retrieve.
      responses:
        '200':
          description: Invoice details.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/InvoiceResponse'
  /?action=CreateInvoice:
    post:
      operationId: createInvoice
      summary: Create Invoice
      description: Create a new invoice in WHMCS.
      tags:
      - Billing
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              allOf:
              - $ref: '#/components/schemas/AuthCredentials'
              - type: object
                required:
                - userid
                properties:
                  userid:
                    type: integer
                    description: The ID of the client to create the invoice for.
                  status:
                    type: string
                    description: Invoice status.
                    default: Unpaid
                  sendinvoice:
                    type: boolean
                    description: Send invoice email to client.
                  paymentmethod:
                    type: string
                    description: Payment method for the invoice.
                  duedate:
                    type: string
                    format: date
                    description: Invoice due date (YYYYMMDD).
                  draft:
                    type: boolean
                    description: Create as draft invoice.
      responses:
        '200':
          description: Invoice created.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CreateInvoiceResponse'
components:
  schemas:
    InvoicesListResponse:
      type: object
      properties:
        result:
          type: string
        totalresults:
          type: integer
        startnumber:
          type: integer
        numreturned:
          type: integer
        invoices:
          type: object
          properties:
            invoice:
              type: array
              items:
                $ref: '#/components/schemas/Invoice'
    CreateInvoiceResponse:
      type: object
      properties:
        result:
          type: string
        invoiceid:
          type: integer
          description: ID of the created invoice.
    InvoiceResponse:
      type: object
      properties:
        result:
          type: string
        invoiceid:
          type: integer
        userid:
          type: integer
        date:
          type: string
          format: date
        duedate:
          type: string
          format: date
        total:
          type: number
          format: float
        status:
          type: string
        items:
          type: object
          properties:
            item:
              type: array
              items:
                type: object
                properties:
                  id:
                    type: integer
                  type:
                    type: string
                  description:
                    type: string
                  amount:
                    type: number
                    format: float
                  taxed:
                    type: integer
    AuthCredentials:
      type: object
      required:
      - identifier
      - secret
      - responsetype
      properties:
        identifier:
          type: string
          description: API credential identifier.
        secret:
          type: string
          description: API credential secret key.
        responsetype:
          type: string
          enum:
          - json
          - xml
          default: json
          description: Response format type.
    Invoice:
      type: object
      properties:
        id:
          type: integer
        userid:
          type: integer
        firstname:
          type: string
        lastname:
          type: string
        companyname:
          type: string
        invoicenum:
          type: string
        date:
          type: string
          format: date
        duedate:
          type: string
          format: date
        datepaid:
          type: string
          format: date
        subtotal:
          type: number
          format: float
        credit:
          type: number
          format: float
        tax:
          type: number
          format: float
        tax2:
          type: number
          format: float
        total:
          type: number
          format: float
        balance:
          type: number
          format: float
        status:
          type: string
          enum:
          - Unpaid
          - Paid
          - Cancelled
          - Refunded
          - Collections
          - Draft
        paymentmethod:
          type: string
  securitySchemes:
    ApiCredentials:
      type: apiKey
      in: query
      name: identifier
      description: WHMCS API credentials. Provide identifier and secret parameters in the POST request body, along with the action parameter.