> ## Documentation Index > Fetch the complete documentation index at: https://docs.arcuserp.com/llms.txt > Use this file to discover all available pages before exploring further. # Upsert a custom-field value > Writes (insert-or-update) a single custom-field value for a parent record. Exactly one of `value_text` / `value_number` / `value_date` / `value_datetime` / `value_boolean` / `value_json` is populated based on the CustomField.field_type. Note: this is the only PUT verb in the public API surface today; the unusual verb reflects the strict upsert semantic. Requires the `custom_fields:write` scope. ## OpenAPI ````yaml /openapi.yaml put /custom_fields/{id}/values/{record_id} openapi: 3.1.0 info: title: Arcus ERP Public API version: 1.0.0 description: > Arcus ERP public REST API. Designed for external integrations and data migration. **Authentication.** Bearer token (API key) via the `Authorization` header. Format: `Authorization: Bearer ark_live_ent__` (or `ark_test_*` for sandbox). API keys are issued per-entity in **Settings > Developers > API Keys**. **Entity scoping.** The entity is encoded in the API key prefix; routes are flat (e.g. `/v1/accounts`, `/v1/orders`, `/v1/products`). A small set of platform endpoints (migration, reconciliation, events, webhook endpoints, API keys) use the `/v1/entities/{entity_id}/...` form -- those are noted in their tags. **Key capabilities.** - Related-resource hydration via `?expand[]=` (see `x-arcus-expand` on each resource). - Cursor-based pagination (`starting_after` / `ending_before` / `limit`). - Idempotency via the `Idempotency-Key` header. - Webhook events for asynchronous notification. - Conditional requests / ETag for cache validation. servers: - url: https://api.arcuserp.com/v1 description: Arcus ERP API (accepts both live `ark_live_*` and test `ark_test_*` keys) - url: https://dev-api.arcuserp.com/v1 description: >- Dev sandbox API (test-only data, accepts `ark_test_*` keys against dev RDS) security: [] paths: /custom_fields/{id}/values/{record_id}: parameters: - name: id in: path required: true schema: type: string format: uuid description: CustomField id. - name: record_id in: path required: true schema: type: string format: uuid description: Parent resource record id. put: tags: - CustomFields summary: Upsert a custom-field value description: | Writes (insert-or-update) a single custom-field value for a parent record. Exactly one of `value_text` / `value_number` / `value_date` / `value_datetime` / `value_boolean` / `value_json` is populated based on the CustomField.field_type. Note: this is the only PUT verb in the public API surface today; the unusual verb reflects the strict upsert semantic. Requires the `custom_fields:write` scope. operationId: setCustomFieldValueV1 requestBody: required: true content: application/json: schema: type: object required: - parent_type - value properties: parent_type: type: string description: Mirrors CustomField.parent_type. value: oneOf: - type: string - type: number - type: boolean - type: object - type: array items: type: string - type: 'null' description: >- Coerced into the matching value_* column per CustomField.field_type. responses: '200': description: Upserted value content: application/json: schema: $ref: '#/components/schemas/CustomFieldValue' '400': description: type_mismatch (value does not satisfy field_type) content: application/json: schema: $ref: '#/components/schemas/Error' '404': description: custom_field_not_found content: application/json: schema: $ref: '#/components/schemas/Error' security: - ApiKeyAuth: - custom_fields:write components: schemas: CustomFieldValue: type: object description: > A custom-field value attached to a parent record (parent_type + parent_id). Exactly ONE of `value_text` / `value_number` / `value_date` / `value_datetime` / `value_boolean` / `value_json` is populated based on the parent CustomField.field_type. Scope: custom_fields:read / custom_fields:write. properties: id: type: string format: uuid readOnly: true object: type: string example: custom_field_value entity_id: type: string format: uuid readOnly: true custom_field_id: type: string format: uuid parent_type: type: string description: Mirrors CustomField.parent_type. parent_id: type: string format: uuid description: Id of the parent resource record. value_text: type: string nullable: true value_number: type: number format: float nullable: true value_date: type: string format: date nullable: true value_datetime: type: string format: date-time nullable: true value_boolean: type: boolean nullable: true value_json: type: object nullable: true created_at: type: string format: date-time readOnly: true updated_at: type: string format: date-time readOnly: true Error: description: | Alias for ErrorEnvelope. Canonical error response shape used by all API endpoints. Refer to ErrorEnvelope for the full field definition. allOf: - $ref: '#/components/schemas/ErrorEnvelope' ErrorEnvelope: type: object description: | Canonical error response envelope. All API errors use this shape. required: - error - code properties: error: type: string description: Machine-readable error key example: not_found code: type: string description: Machine-readable error code (often same as error) example: not_found type: type: string enum: - validation_error - permission_error - not_found - conflict - rate_limit - internal - expand_error - not_implemented example: not_found hint: type: string description: Human-readable one-sentence explanation (English) example: >- The requested order does not exist or does not belong to this entity. param: type: string description: The parameter that caused the error, if applicable example: expand[0] required: type: string description: The scope required (only on insufficient_scope errors) example: accounts:read request_id: type: string description: >- Unique request ID for support tracing (maps to CloudWatch log stream) example: req_abc123 securitySchemes: ApiKeyAuth: type: http scheme: bearer description: | API key issued per entity via Settings > Developers > API Keys. Each key carries scopes (e.g. orders:read, products:write). Bearer token format: Authorization: Bearer ark_live_ent__ Test keys use ark_test_ent__. Both are issued per entity via Settings > Developers > API Keys. ````