> ## Documentation Index > Fetch the complete documentation index at: https://docs.ionicfi.com/llms.txt > Use this file to discover all available pages before exploring further. # Set default payment method > Sets or clears the customer's default payment method. Pass `null` for `default_payment_method` to clear it. The method must already be attached to the customer. ## OpenAPI ````yaml /openapi/customers.yaml post /customers/{id}/default_payment_method openapi: 3.0.3 info: title: Ionic Customers API version: '2026-05-01' description: | Customer profiles — the anchor for payment methods, invoices, and subscriptions. A customer (`cus_…`) represents a single payer stored under your merchant account. It holds contact information (email, name, phone), optional billing and shipping addresses, and a link to a default payment method. Invoices and subscriptions reference customers by id; payment methods are attached to customers and become available for off-session charges. All timestamps are Unix epoch seconds. Identifiers are opaque, prefixed strings. Authentication uses a merchant secret key (`sk_…`) as a bearer token. Read endpoints require the `customers:read` permission; write endpoints require `customers:write`. The mode of the key (test or live) scopes which customers it can see and mutate. Customers support soft-delete: a deleted customer has `deleted: true` and cannot be modified until restored. Write endpoints that target a deleted customer return `422`. To undo a deletion, call the restore endpoint. Errors are returned as `{ "error": { "code": "...", "message": "..." } }`. servers: - url: '{baseUrl}/v1' variables: baseUrl: default: https://api.ionicfi.com description: API base URL for your environment. security: - secretKey: [] tags: - name: Customers description: Create, retrieve, update, and manage customer profiles. paths: /customers/{id}/default_payment_method: parameters: - $ref: '#/components/parameters/CustomerId' - $ref: '#/components/parameters/IonicAccount' post: tags: - Customers summary: Set default payment method description: >- Sets or clears the customer's default payment method. Pass `null` for `default_payment_method` to clear it. The method must already be attached to the customer. operationId: customers_set_default_payment_method parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/SetDefaultPaymentMethodRequest' responses: '200': description: The updated customer. content: application/json: schema: $ref: '#/components/schemas/Customer' '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/CustomerNotFound' '429': $ref: '#/components/responses/RateLimited' '500': $ref: '#/components/responses/InternalError' security: - secretKey: - customers:write components: parameters: CustomerId: name: id in: path required: true description: The customer id (`cus_…`). schema: type: string IonicAccount: name: Ionic-Account in: header required: false description: | Merchant ID when an authorized Platform acts for a connected Merchant. Omit when authenticating directly as that Merchant. schema: type: string pattern: ^mer_[0-9A-Za-z]{14}$ IdempotencyKey: name: Idempotency-Key in: header required: false description: >- A unique key that makes retries safe: the same key with the same request body returns the original response instead of repeating the operation. schema: type: string maxLength: 255 schemas: SetDefaultPaymentMethodRequest: type: object properties: default_payment_method: type: string nullable: true description: Payment method id (`pm_…`). Pass `null` to clear the default. Customer: type: object required: - billing_address - created_at - creation_source - deleted - email - first_name - id - last_name - livemode - merchant_id - metadata - object - payment_settings - phone - shipping - test_clock - updated_at properties: id: type: string description: Unique customer identifier (`cus_…`). object: type: string enum: - customer merchant_id: type: string livemode: type: boolean description: >- Whether this customer was created with a live (`true`) or test (`false`) key. test_clock: type: string nullable: true description: >- The immutable logical billing clock attached at creation; null when this customer uses wall-clock time. email: type: string first_name: type: string description: Empty string when not set. last_name: type: string description: Empty string when not set. phone: type: string description: Empty string when not set. billing_address: allOf: - $ref: '#/components/schemas/Address' nullable: true description: Billing address; null when not set. shipping: allOf: - $ref: '#/components/schemas/ShippingDetails' nullable: true description: Shipping details; null when not set. creation_source: type: string enum: - api - checkout - import - dashboard - platform description: How the customer was created (for example `api`). payment_settings: $ref: '#/components/schemas/PaymentSettings' metadata: type: object additionalProperties: type: string deleted: type: boolean description: True when the customer has been soft-deleted. created_at: type: integer description: Unix epoch seconds. updated_at: type: integer Address: type: object required: - city - country - line1 - postal_code - state properties: line1: type: string line2: type: string description: Second address line; absent when not set. city: type: string state: type: string postal_code: type: string country: type: string description: ISO 3166-1 alpha-2 country code. ShippingDetails: type: object required: - address - name - phone properties: name: type: string description: Recipient name. phone: type: string description: Recipient phone number. address: $ref: '#/components/schemas/Address' PaymentSettings: type: object description: Payment configuration stored for the customer. properties: default_payment_method: type: string description: The default payment method id (`pm_…`); absent when none is set. Error: type: object properties: error: type: object properties: code: type: string description: A stable, machine-readable error code. message: type: string responses: BadRequest: description: The request was malformed or failed validation. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: INVALID_REQUEST message: invalid request body Unauthorized: description: Missing or invalid API key. content: application/json: schema: $ref: '#/components/schemas/Error' Forbidden: description: The key lacks the required permission, or the merchant is not active. content: application/json: schema: $ref: '#/components/schemas/Error' CustomerNotFound: description: No customer with that id is visible to this key. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: CUSTOMER_NOT_FOUND message: customer not found RateLimited: description: Too many requests. Honour the `Retry-After` header before retrying. content: application/json: schema: $ref: '#/components/schemas/Error' InternalError: description: | The API could not return a successful response. For a mutating request, retrieve the resource before retrying because the operation may have completed. content: application/json: schema: $ref: '#/components/schemas/Error' securitySchemes: secretKey: type: http scheme: bearer description: 'A merchant secret key (`sk_…`) sent as `Authorization: Bearer `.' ````