> ## Documentation Index > Fetch the complete documentation index at: https://docs.grainfinance.co/llms.txt > Use this file to discover all available pages before exploring further. # Create Customer > Creates a new customer. If a customer with the same external ID already exists, the record is updated automatically. ## OpenAPI ````yaml POST /customers openapi: 3.1.0 info: title: Grain API version: 1.0.0 description: >- Grain's API provides a comprehensive set of endpoints for managing hedging, spot transactions, pricing, and fund movements - enabling seamless integration of FX workflows into your platform. Each API call follows REST conventions, uses secure authentication, and returns standardized responses for consistency across environments. license: name: Creative Commons Attribution 3.0 contact: name: Grain Finance url: https://docs.grainfinance.co email: support@grainfinance.co termsOfService: https://grainfinance.co/terms-of-service/ x-apiClientRegistration: url: https://grainfinance.co/partners servers: - url: https://api.grainfinance.co/v1 description: Grain API security: [] tags: - name: Hedges description: >- Hedge objects represent transactions that lock exchange rates for future dates. A single hedge locks an exchange rate for a future transaction between two currencies. - name: Dual Hedges description: >- A dual hedge mitigates FX risk by automatically generating two linked hedge legs - a customer leg and a supplier leg - both routed through the customer's functional currency. This structure reduces exposure to currency fluctuations for both cash flow and accounting purposes, while allowing independent tracking and reporting of each hedge leg. - name: Customers description: >- Customer objects represent your end customers on the Grain platform. A customer must be created before a hedge or spot transaction can be initiated. - name: Pricing description: >- Pricing endpoints provide access to FX rates for currency pairs that are not being hedged. These endpoints can be used for live rate display or bulk retrieval to support high-volume quoting workflows. - name: Spots description: >- Spot objects represent currency conversions executed for immediate or near-term settlement. - name: Conversions description: >- Conversion objects represent currency conversions executed for immediate or near-term settlement. - name: Wallets description: Endpoints to view balances, manage funding, and perform transfers. paths: /customers: post: tags: - Customers description: >- Creates a new customer. If a customer with the same external ID already exists, the record is updated automatically. operationId: Create parameters: [] requestBody: description: The payload required in order to create a customer required: true content: application/json: schema: $ref: '#/components/schemas/CreateUpdateCustomerRequestBody' description: The payload required in order to create a customer responses: '200': description: Customer Updated content: application/json: schema: $ref: '#/components/schemas/CreateObjectResponseBody' '201': description: Customer Created content: application/json: schema: $ref: '#/components/schemas/CreateObjectResponseBody' '400': description: >- The request failed because it is not well-formed or is syntactically incorrect or violates schema. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '422': description: >- The request failed because it is either semantically incorrect or has failed business validation. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - api-key: [] components: schemas: CreateUpdateCustomerRequestBody: $ref: >- #/components/schemas/Pick_Customer.-or-contactEmail-or-contactFullName-or-contactPhoneNumber-or-companyName-or-companyAddress-or-companyCity-or-companyState-or-companyCountry-or-companyTaxId-or-externalCustomerId-or-extraFields_ CreateObjectResponseBody: description: A response containing the ID of the created object. properties: id: $ref: '#/components/schemas/UUID' description: The id of the created object. example: 1b0ada1e-fa1b-4cfe-a553-01b340c5650e required: - id type: object additionalProperties: false ErrorResponse: description: An API Error properties: message: type: string description: A short explanation of the error. example: Can't perform this action reason: type: string description: A detailed description of the reason for the failure. example: >- Supplied object is in *Cancelled* state, which prevents performing this action required: - message type: object additionalProperties: false Pick_Customer.-or-contactEmail-or-contactFullName-or-contactPhoneNumber-or-companyName-or-companyAddress-or-companyCity-or-companyState-or-companyCountry-or-companyTaxId-or-externalCustomerId-or-extraFields_: properties: contactEmail: $ref: '#/components/schemas/ContactEmail' description: The email for the company's primary contact example: customer@company.com contactFullName: type: string description: The name of the company's primary contact example: Garrick Ollivander contactPhoneNumber: type: string description: The phone number of the company's primary contact example: '+12125551234' companyName: type: string description: The legal name of the customer's company example: Ollivander's Wand Shop companyAddress: type: string description: The address of the company example: 12 Diagon Alley companyCity: type: string description: The city of the company example: London companyState: type: string description: The state the company is in (US based) example: London companyCountry: $ref: '#/components/schemas/CountryCode' companyTaxId: type: string description: The tax identification or registration number of the company example: 123-45-6789 externalCustomerId: type: string description: The id used to identify the customer within your platform example: 630231b3ae0d7e9e5097ad35 extraFields: $ref: '#/components/schemas/CustomersExtraFieldsParam' description: |- Additional fields that provide further details about the customer. These fields should be specified as a valid JSON object. example: field_a: value_a field_b: value_b required: - companyName - companyCountry - externalCustomerId type: object description: From T, pick a set of properties whose keys are in the union K UUID: type: string format: uuid description: |- Stringified UUIDv4. See [RFC 4112](https://tools.ietf.org/html/rfc4122) pattern: >- [0-9A-Fa-f]{8}-[0-9A-Fa-f]{4}-4[0-9A-Fa-f]{3}-[89ABab][0-9A-Fa-f]{3}-[0-9A-Fa-f]{12} ContactEmail: type: string example: garrick@ollivanders.co.uk description: The email address of the company's primary contact CountryCode: type: string example: GB description: The alpha-2 ISO 3166 country code of the entity's country. pattern: ^[A-Za-z]{2}$ CustomersExtraFieldsParam: properties: {} additionalProperties: anyOf: - type: string - type: number format: double - type: boolean type: object example: field_a: value_a field_b: value_b description: |- Additional fields that provide further details about the company. These fields should be specified as a valid JSON object. securitySchemes: api-key: type: http scheme: basic description: >- Basic authentication using the partner API keys from https://console.grainfinance.co/keys ````