> ## Documentation Index > Fetch the complete documentation index at: https://docs.server.express/llms.txt > Use this file to discover all available pages before exploring further. # Pay an invoice > Starts or completes payment, depending on `method`: - `credit` — converts the total to GBP at the current rate, deducts it from the credit balance, records the payment and settles the invoice immediately. 400 if the balance is short; 503 if no exchange rate is available. - `stripe` (default when cards are on) — creates a Stripe Checkout session and a pending payment; redirect to `url`. 409 when card payments are switched off. - `crypto` (`nowpayments`, `heleket`, `paykilla` accepted as aliases) — creates an inline payment on the active gateway for the coin in `toCurrency` and a pending payment row. 400 if no gateway is configured or `toCurrency` is missing. With cards off and no `method`, returns 400 listing `availableMethods`. Paid → 400; cancelled/refunded or inside an open combined invoice → 409. Drafts return 404. Requires a complete billing address (428). An invalid JSON body is treated as empty. Unexpected failures return 500 with the underlying error message. ## OpenAPI ````yaml /api-reference/openapi.yaml post /v1/client/invoices/{id}/pay openapi: 3.1.0 info: title: Server.Express API version: 1.0.0 description: >- The customer-facing Server.Express API: auth, billing, tickets, cloud and dedicated servers, hosting, reselling and account management. Every response uses the `{ success, data | error }` envelope. contact: name: Server.Express url: https://server.express servers: - url: https://my.server.express/api description: Production security: - bearerAuth: [] - apiToken: [] tags: - name: API Tokens - name: Account - name: Auth - name: Cloud - name: Coupons - name: Credits - name: Dashboard - name: Dedicated - name: Health - name: Hosting - name: Integrations - name: Invoices - name: Livechat - name: Notifications - name: Passkeys - name: Payments - name: Products - name: Public - name: Public Invoices - name: Public Tools - name: Reseller - name: SSH Keys - name: Services - name: Tasks - name: Teams - name: Tickets - name: Web Hosting - name: Webhooks paths: /v1/client/invoices/{id}/pay: parameters: - name: id in: path required: true schema: type: string format: uuid post: tags: - Invoices summary: Pay an invoice description: >- Starts or completes payment, depending on `method`: - `credit` — converts the total to GBP at the current rate, deducts it from the credit balance, records the payment and settles the invoice immediately. 400 if the balance is short; 503 if no exchange rate is available. - `stripe` (default when cards are on) — creates a Stripe Checkout session and a pending payment; redirect to `url`. 409 when card payments are switched off. - `crypto` (`nowpayments`, `heleket`, `paykilla` accepted as aliases) — creates an inline payment on the active gateway for the coin in `toCurrency` and a pending payment row. 400 if no gateway is configured or `toCurrency` is missing. With cards off and no `method`, returns 400 listing `availableMethods`. Paid → 400; cancelled/refunded or inside an open combined invoice → 409. Drafts return 404. Requires a complete billing address (428). An invalid JSON body is treated as empty. Unexpected failures return 500 with the underlying error message. operationId: publicClientPayInvoice requestBody: required: false content: application/json: schema: type: object properties: method: type: string enum: - stripe - credit - crypto - nowpayments - heleket - paykilla toCurrency: type: string description: >- Required for crypto. NowPayments-style ticker, e.g. btc or usdttrc20. network: type: string description: Accepted but currently unused. responses: '200': description: Payment started (stripe, crypto) or completed (credit). content: application/json: schema: type: object required: - success - data properties: success: type: boolean const: true data: oneOf: - type: object required: - method - paid - deductedGbp properties: method: type: string const: credit paid: type: boolean const: true deductedGbp: type: integer description: Credit taken, GBP minor units. - type: object required: - method - url properties: method: type: string const: stripe url: type: - string - 'null' format: uri description: Stripe Checkout URL. - $ref: '#/components/schemas/PublicClientCryptoPayment' '400': description: >- Already paid, short of credit, no crypto gateway, no coin chosen, unsupported method, or no method while cards are off. content: application/json: schema: allOf: - $ref: '#/components/schemas/ErrorResponse' - type: object properties: data: type: object properties: availableMethods: type: array items: type: string enum: - credit - crypto '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/NotFound' '409': description: >- Invoice is closed or covered by a combined invoice, or card payments are switched off. content: application/json: schema: $ref: '#/components/schemas/PublicClientInvoiceBlockedError' '428': description: The account has no complete billing address yet. content: application/json: schema: $ref: '#/components/schemas/PublicClientBillingDetailsRequired' '500': $ref: '#/components/responses/ServerError' '503': description: >- No exchange rate to convert GBP credit into the invoice currency right now. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - bearerAuth: [] - apiToken: [] components: schemas: PublicClientCryptoPayment: type: object required: - method - gateway - paymentId - address - payerAmount - payerCurrency - network - extraId - expiresAt - paymentStatus - checkoutUrl properties: method: type: string const: crypto gateway: type: string enum: - paykilla - nowpayments paymentId: type: string description: Gateway payment id — pass it to GET /pay?paymentId= to poll. address: type: - string - 'null' description: >- Deposit address to pay to. Null when the customer finishes on the gateway's page instead. payerAmount: type: - number - 'null' payerCurrency: type: - string - 'null' network: type: - string - 'null' extraId: type: - string - 'null' description: Memo/tag some chains require alongside the address. expiresAt: type: - string - 'null' format: date-time paymentStatus: type: string description: NowPayments vocabulary, whichever gateway answered. checkoutUrl: type: - string - 'null' format: uri description: Set when the customer pays on the gateway's own page (PayKilla). ErrorResponse: type: object required: - success - error properties: success: type: boolean const: false error: type: string description: Human-readable error message. additionalProperties: true PublicClientInvoiceBlockedError: type: object description: >- When the invoice is inside an open combined invoice, `data` names the one to pay instead. required: - success - error properties: success: type: boolean const: false error: type: string data: type: object properties: payInsteadInvoiceId: type: string format: uuid payInsteadInvoiceNumber: type: string PublicClientBillingDetailsRequired: type: object description: >- 428 Precondition Required — add the listed billing fields before ordering or paying. required: - success - error - data properties: success: type: boolean const: false error: type: string data: type: object required: - billingDetailsRequired - missing properties: billingDetailsRequired: type: boolean const: true missing: type: array items: type: string enum: - addressLine1 - city - postcode - country - companyName responses: Unauthorized: description: Missing, invalid or expired credentials. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' Forbidden: description: >- Authenticated but not allowed (missing scope, not an admin, or not your resource). content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' NotFound: description: The resource doesn't exist or isn't visible to you. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' ServerError: description: Unexpected server error. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: JWT description: >- Session access token (JWT) from POST /v1/auth/login or /v1/auth/refresh. A session satisfies every API scope. apiToken: type: http scheme: bearer bearerFormat: se_live__ description: >- Personal API token created under Settings → API tokens. Only routes guarded by verifyApiAuth accept it, and the token must carry the scope named in the operation's x-required-scope. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.