Version: v2

Single Payment Flow

🔒 InternalInternal information — not visible in the public (merchant) site.

Overview

A single-allocation payment charges one payment method for the full transaction amount. This is the most common payment flow. The paymentAllocations array contains exactly 1 entry.

Key characteristics:

One allocation — no rollback logic needed
Idempotent via merchantTransactionId (up to 5 attempts)
Supports CARD and BANK_ACCOUNT payment methods
Supports both SALE (immediate charge) and PRE-AUTH (hold then capture) for cards

Sequence Diagram

API Request

info

For complete field definitions and constraints, see the Create Payment API Spec.

Pay with Wallet (Stored Payment Method)

Uses paymentMethodId to reference a card already stored in the customer's wallet.

Sample Request

curl -X POST "https://api-stg.uhg.com/api/financial/commerce/nonprodcheckout/v2/payments" \
  -H "Authorization: Bearer <token>" \
  -H "X-Merchant-Id: b955db5e-aef2-47de-bbb9-c80b9cc16e8f" \
  -H "X-Upstream-Env: dev" \
  -H "Content-Type: application/json" \
  -d '{
    "merchantTransactionId": "order-20260404-001",
    "amount": 15000,
    "currencyCode": "USD",
    "authorizeCard": false,
    "partialAuthorization": false,
    "description": "Payment for order #12345",
    "statementDescriptorSuffix": "ORDER123",
    "customer": {
      "hsid": "b313c1d1-b5b6-4ec7-8b5a-3a9cf7755060",
      "firstName": "John",
      "lastName": "Doe",
      "email": "john.doe@example.com"
    },
    "paymentAllocations": [
      {
        "amount": 15000,
        "paymentMethodId": "b0b3c48d-4cf6-404a-a554-e14640a51c5b"
      }
    ],
    "metadata": {
      "orderId": "12345",
      "channel": "web"
    }
  }'

One-Time Pay (Inline Payment Method)

Provides payment method details inline — the method is not saved to the wallet.

Sample Request

curl -X POST "https://api-stg.uhg.com/api/financial/commerce/nonprodcheckout/v2/payments" \
  -H "Authorization: Bearer <token>" \
  -H "X-Merchant-Id: b955db5e-aef2-47de-bbb9-c80b9cc16e8f" \
  -H "X-Upstream-Env: dev" \
  -H "Content-Type: application/json" \
  -d '{
    "merchantTransactionId": "order-20260404-002",
    "amount": 5000,
    "currencyCode": "USD",
    "authorizeCard": false,
    "partialAuthorization": false,
    "customer": {
      "enterpriseIdentifier": "123456789"
    },
    "paymentAllocations": [
      {
        "amount": 5000,
        "paymentMethod": {
          "type": "CARD",
          "card": {
            "number": "4242424242424242",
            "expMonth": 12,
            "expYear": 2028,
            "cvc": "123"
          }
        }
      }
    ]
  }'

API Response

202 Accepted (Immediate Response)

The service returns 202 immediately with the payment in INITIATED or PENDING state.

{
  "url": "https://api-stg.uhg.com/api/financial/commerce/nonprodcheckout/v2/payments/550e8400-e29b-41d4-a716-446655440000",
  "data": {
    "id": "550e8400-e29b-41d4-a716-446655440000",
    "merchantTransactionId": "order-20260404-001",
    "amount": 15000,
    "currencyCode": "USD",
    "status": "INITIATED",
    "authorizeCard": false,
    "authRequired": false,
    "partialAuthorization": false,
    "statementDescriptorSuffix": "ORDER123",
    "description": "Payment for order #12345",
    "customer": {
      "firstName": "John",
      "lastName": "Doe",
      "email": "john.doe@example.com",
      "hsid": "b313c1d1-b5b6-4ec7-8b5a-3a9cf7755060"
    },
    "paymentAllocations": null,
    "paymentDateUtc": "2026-04-04T10:30:00Z",
    "metadata": {
      "orderId": "12345",
      "channel": "web"
    }
  }
}

200 OK — Completed Payment (GET)

After processing completes, a GET /v2/payments/{paymentId} returns the full result:

{
  "url": "https://api-stg.uhg.com/api/financial/commerce/nonprodcheckout/v2/payments/550e8400-e29b-41d4-a716-446655440000",
  "data": {
    "id": "550e8400-e29b-41d4-a716-446655440000",
    "merchantTransactionId": "order-20260404-001",
    "amount": 15000,
    "authorizedAmount": 15000,
    "capturedAmount": 15000,
    "currencyCode": "USD",
    "status": "COMPLETED",
    "authorizeCard": false,
    "authRequired": false,
    "partialAuthorization": false,
    "statementDescriptorSuffix": "ORDER123",
    "description": "Payment for order #12345",
    "customer": {
      "firstName": "John",
      "lastName": "Doe",
      "email": "john.doe@example.com",
      "hsid": "b313c1d1-b5b6-4ec7-8b5a-3a9cf7755060"
    },
    "paymentAllocations": [
      {
        "id": "a1b2c3d4-e5f6-7890-1234-567890abcdef",
        "amount": 15000,
        "authorizedAmount": 15000,
        "capturedAmount": 15000,
        "status": "COMPLETED",
        "paymentMethod": {
          "id": "b0b3c48d-4cf6-404a-a554-e14640a51c5b",
          "type": "CARD",
          "card": {
            "lastFour": "4242",
            "brand": "visa",
            "expMonth": 12,
            "expYear": 2028
          }
        },
        "vendor": {
          "name": "STRIPE",
          "transactionId": "pi_3NabcXYZ123456789"
        }
      }
    ],
    "paymentDateUtc": "2026-04-04T10:30:00Z",
    "metadata": {
      "orderId": "12345",
      "channel": "web"
    },
    "merchant": {
      "id": "b955db5e-aef2-47de-bbb9-c80b9cc16e8f",
      "name": "Example Merchant"
    }
  }
}

Validation Rules

Rule	HTTP Status	Error
`paymentAllocations` array must have exactly 1 item (single payment)	400	`INVALID_REQUEST`
`paymentAllocations[0].amount` must equal top-level `amount`	400	`INVALID_REQUEST`
`amount` must be ≥ 1 and ≤ 100,000,000	400	`INVALID_REQUEST`
`merchantTransactionId` must be 1-50 characters	400	`INVALID_REQUEST`
Each allocation must have either `paymentMethodId` OR `paymentMethod`, not both	400	`INVALID_REQUEST`
`authorizeCard: true` requires `partialAuthorization: true`	400	`INVALID_REQUEST`
Customer must have at least one identifier (`hsid`, `enterpriseIdentifier`, or `metadata`)	400	`INVALID_REQUEST`

Error Scenarios

400 — Bad Request (Schema Validation)

{
  "title": "INVALID_REQUEST",
  "status": 400,
  "detail": "Invalid request format. Please check JSON structure and field types"
}

403 — Forbidden (Merchant Not Linked)

{
  "title": "FORBIDDEN",
  "status": 403,
  "detail": "403 FORBIDDEN. RequestId: abc123-def456"
}

422 — Unprocessable Entity (Payment Failed)

{
  "title": "PAYMENT_ERROR",
  "status": 422,
  "detail": "Payment processing failed for all records. Check individual records for error details",
  "data": {
    "id": "550e8400-e29b-41d4-a716-446655440000",
    "merchantTransactionId": "order-20260404-001",
    "amount": 15000,
    "status": "FAILED",
    "paymentAllocations": [
      {
        "id": "a1b2c3d4-e5f6-7890-1234-567890abcdef",
        "amount": 15000,
        "status": "FAILED",
        "error": {
          "code": "card_declined",
          "message": "Your card was declined."
        }
      }
    ]
  }
}

Webhook Payload — PAYMENT_SUCCEEDED

{
  "name": "PAYMENT_SUCCEEDED",
  "source": "merchant-portal",
  "payload": {
    "id": "550e8400-e29b-41d4-a716-446655440000",
    "merchantTransactionId": "order-20260404-001",
    "amount": 15000,
    "currencyCode": "USD",
    "status": "COMPLETED",
    "customer": {
      "firstName": "John",
      "lastName": "Doe",
      "email": "john.doe@example.com"
    },
    "paymentAllocations": [
      {
        "id": "a1b2c3d4-e5f6-7890-1234-567890abcdef",
        "amount": 15000,
        "status": "COMPLETED",
        "paymentMethod": {
          "type": "CARD",
          "card": {
            "lastFour": "4242",
            "brand": "visa"
          }
        }
      }
    ],
    "paymentDateUtc": "2026-04-04T10:30:00Z"
  }
}

Edge Cases

Scenario	Behavior	Notes
Duplicate `merchantTransactionId` (retry ≤ 5)	Returns existing payment with current status	No new processing; idempotent response
Duplicate `merchantTransactionId` (retry > 5)	`422 UNPROCESSABLE_ENTITY`	Merchant must generate a new ID
Stripe timeout	Allocation marked `FAILED`, payment marked `FAILED`	Circuit breaker may open if repeated
Customer not found	Payment transitions to `PENDING_FOR_CUSTOMER_CREATION` then `FAILED`	Error logged with resolution details
Invalid `paymentMethodId`	`422 UNPROCESSABLE_ENTITY`	PM must exist in customer's wallet
Expired card	`422 PAYMENT_ERROR` with vendor error	Allocation error contains decline reason

Overview​

Sequence Diagram​

API Request​

Pay with Wallet (Stored Payment Method)​

One-Time Pay (Inline Payment Method)​

API Response​

202 Accepted (Immediate Response)​

200 OK — Completed Payment (GET)​

Validation Rules​

Error Scenarios​

400 — Bad Request (Schema Validation)​

403 — Forbidden (Merchant Not Linked)​

422 — Unprocessable Entity (Payment Failed)​

Webhook Payload — PAYMENT_SUCCEEDED​

Edge Cases​

Related Documentation​