> ## Documentation Index > Fetch the complete documentation index at: https://documentation.qonversion.io/llms.txt > Use this file to discover all available pages before exploring further. # Set customer properties > Sets one or more custom properties on a customer. Accepts up to 100 key/value pairs per request. Keys must be 1–256 characters; values must be at most 1024 characters. ## OpenAPI ````yaml /api-reference/rest-api-v4.yaml post /customers/{customer_id}/properties openapi: 3.0.3 info: title: Qonversion REST API v4 version: '4.0' description: >- Qonversion REST API v4 follows REST standards. It has predictable resource-oriented URLs, accepts JSON-encoded request bodies, returns JSON-encoded responses, and uses standard HTTP response codes, authentication, and verbs. servers: - url: https://api.qonversion.io/v4 description: Production security: - secretAuth: [] tags: - name: Users description: Retrieve Qonversion users - name: User Properties description: Manage user-level attributes - name: Identities description: Link Qonversion users to your own auth IDs - name: Entitlements description: Entitlement definitions and user grants - name: Purchases description: A user's purchase history - name: Products description: Products configured in the Qonversion dashboard - name: Customers description: Aggregated customer records, properties, permissions, and metrics - name: Segments description: Dynamic and system segments of users - name: Experiments description: Paywall and offering A/B experiments - name: Screens description: No-code paywall screens — CRUD, publish, analytics - name: Analytics description: Charts, cards, cohorts, LTV, and insights - name: Exports description: Asynchronous data exports - name: Events description: Event catalog - name: Scheduled Reports description: Recurring reports delivered to external destinations - name: Integrations description: Third-party integrations configuration - name: Automations description: Event-driven automations - name: Project Settings description: Project-level configuration, secret, and store credentials paths: /customers/{customer_id}/properties: post: tags: - Customers summary: Set customer properties description: | Sets one or more custom properties on a customer. Accepts up to 100 key/value pairs per request. Keys must be 1–256 characters; values must be at most 1024 characters. operationId: v4SetCustomerProperties parameters: - name: customer_id in: path required: true schema: type: string description: Customer identifier. example: customer_abc123 requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/V4CustomerPropertiesRequest' responses: '200': description: Properties set successfully. Returns updated customer data. headers: Cache-Control: schema: type: string example: no-cache content: application/json: schema: type: object description: >- Property-save result wrapped in the v4 envelope (object, url, data). `data.saved_properties` lists the (key, value) pairs that were accepted; `data.property_errors` lists any rejected pairs with the reason — both are always present, empty arrays on success. example: object: customer_properties url: /v4/customers/customer_abc123/properties data: saved_properties: - key: plan_tier value: premium - key: referral_source value: email_campaign property_errors: [] '400': description: Invalid request content: application/json: schema: $ref: '#/components/schemas/V4Error' '401': description: Unauthorized content: application/json: schema: $ref: '#/components/schemas/V4Error' '404': description: Customer not found content: application/json: schema: $ref: '#/components/schemas/V4Error' '415': description: Unsupported Content-Type content: application/json: schema: $ref: '#/components/schemas/V4Error' '429': description: Too many requests content: application/json: schema: $ref: '#/components/schemas/V4Error' '500': description: Internal error content: application/json: schema: $ref: '#/components/schemas/V4Error' '502': description: Storage error content: application/json: schema: $ref: '#/components/schemas/V4Error' '504': description: Upstream timeout content: application/json: schema: $ref: '#/components/schemas/V4Error' security: - secretAuth: [] components: schemas: V4CustomerPropertiesRequest: type: object required: - properties properties: properties: type: array description: >- List of key/value property pairs to set on the customer. 1–100 items. minItems: 1 maxItems: 100 items: type: object required: - key - value properties: key: type: string description: Property key. 1–256 characters. minLength: 1 maxLength: 256 example: plan_tier value: type: string description: Property value. At most 1024 characters. maxLength: 1024 example: premium V4Error: type: object required: - error properties: error: type: object required: - type - code - message properties: type: type: string enum: - request - resource - logical - internal code: type: string description: | Machine-readable snake_case error code. Examples include `invalid_data`, `invalid_request`, `invalid_product_id`, `not_found`, `already_exists`, `offering_already_exists`, `product_not_in_project`, `cannot_set_main_directly`, `cannot_demote_main`, `cannot_patch_experiment_variant`, `cannot_delete_experiment_variant`, and `cannot_setmain_experiment_variant`. Resource-specific codes are documented on the corresponding reference page. message: type: string description: Human-readable description. May change; do not parse. details: type: array nullable: true description: Per-field validation errors, present on 400 validation failures. items: type: object properties: field: type: string message: type: string securitySchemes: secretAuth: type: http scheme: bearer bearerFormat: sk_… description: >- Bearer authentication using the project **Secret Key** (prefixed with `sk_`, or `test_sk_` for sandbox). All v4 public endpoints require the Secret Key — see [Authentication](/reference/v4/authentication). Never expose the Secret Key in client-side code. ````