Interswitch Web Checkout API

openapi: 3.1.0
info:
  title: Interswitch Web Checkout API
  description: |
    Interswitch Web Checkout (formerly Webpay) is the company's hosted payment
    gateway. Two integration modes are supported: an inline JavaScript popup
    loaded from `inline-checkout.js`, and a Web Redirect form POST to
    `/collections/w/pay`. After payment, merchants must perform a server-side
    requery against `/collections/api/v1/gettransaction.json` and verify both
    the response code (`00`) and the returned amount before delivering value.
  version: '2024-01-01'
  contact:
    name: Interswitch Developer Support
    url: https://www.interswitchgroup.com/support
servers:
  - url: https://sandbox.interswitchng.com
    description: Sandbox
  - url: https://newwebpay.interswitchng.com
    description: Production
security:
  - InterswitchAuth: []
tags:
  - name: Checkout
    description: Hosted checkout payment initiation
  - name: Transactions
    description: Transaction status query
paths:
  /collections/w/pay:
    post:
      tags: [Checkout]
      summary: Initiate Web Redirect Payment
      description: |
        POST an HTML form (`application/x-www-form-urlencoded`) to redirect the
        customer to the Interswitch hosted payment page. After payment, the
        browser is redirected back to `site_redirect_url` with `txnref` in the
        query string. Always confirm the transaction server-side via
        `/collections/api/v1/gettransaction.json` before delivering value.
      operationId: initiateWebRedirectPayment
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              $ref: '#/components/schemas/CheckoutRequest'
      responses:
        '302':
          description: Redirect to hosted payment page.
        '400':
          description: Validation error in the submitted form.
  /collections/api/v1/gettransaction.json:
    get:
      tags: [Transactions]
      summary: Get Transaction Status
      description: |
        Server-side transaction requery. Returns the authoritative status,
        response code, and amount for a given transaction reference. Must be
        called before delivering value; do not rely on the browser redirect
        parameters.
      operationId: getTransactionStatus
      parameters:
        - in: query
          name: merchantcode
          required: true
          schema: { type: string }
          description: Merchant code issued by Interswitch.
        - in: query
          name: transactionreference
          required: true
          schema: { type: string }
          description: Original `txn_ref` submitted at checkout.
        - in: query
          name: amount
          required: true
          schema: { type: integer }
          description: Original transaction amount in minor units (kobo).
      responses:
        '200':
          description: Transaction status.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/TransactionStatus'
components:
  securitySchemes:
    InterswitchAuth:
      type: apiKey
      in: header
      name: Authorization
      description: |
        Either `InterswitchAuth {base64(client_id)}` with companion `Timestamp`,
        `Nonce`, `Signature`, and `SignatureMethod` headers (legacy), or
        `Bearer {access_token}` obtained from the Passport OAuth token endpoint.
  schemas:
    CheckoutRequest:
      type: object
      required: [merchant_code, pay_item_id, txn_ref, amount, currency, cust_email, site_redirect_url]
      properties:
        merchant_code: { type: string, description: Merchant identifier from Quickteller Business. }
        pay_item_id: { type: string, description: Pay item identifier configured on the merchant account. }
        txn_ref: { type: string, description: Unique merchant transaction reference. }
        amount: { type: integer, description: Amount in minor currency units (e.g. kobo for NGN). }
        currency: { type: string, description: ISO 4217 numeric currency code (e.g. 566 for NGN). }
        cust_email: { type: string, format: email }
        site_redirect_url: { type: string, format: uri }
    TransactionStatus:
      type: object
      properties:
        ResponseCode: { type: string, description: '00 indicates a successful, approved transaction.' }
        Amount: { type: integer, description: Settled amount in minor units. }
        TransactionDate: { type: string, format: date-time }
        MerchantReference: { type: string }
        PaymentReference: { type: string }
        RetrievalReferenceNumber: { type: string }
        CardNumber: { type: string, description: Masked PAN of the card used. }
        LeadBankCbnCode: { type: string }
        LeadBankName: { type: string }