> ## 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. # Update a custom field definition ## OpenAPI ````yaml /openapi.yaml patch /custom_fields/{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}: parameters: - name: id in: path required: true schema: type: string format: uuid patch: tags: - CustomFields summary: Update a custom field definition operationId: updateCustomFieldV1 parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object properties: label: type: string required: type: boolean options: type: array items: type: string nullable: true default_value: type: string nullable: true help_text: type: string nullable: true display_order: type: integer is_active: type: boolean metadata: type: object responses: '200': description: Updated custom field content: application/json: schema: $ref: '#/components/schemas/CustomField' '400': $ref: '#/components/responses/Error' '404': $ref: '#/components/responses/Error' security: - ApiKeyAuth: - custom_fields:write components: parameters: IdempotencyKey: name: Idempotency-Key in: header required: false description: | Client-generated unique key for idempotent POST/PATCH/DELETE operations. Alias for the Idempotency parameter. Max 255 chars. On retry with the same key, the original response is returned without re-executing the operation. Keys expire after 24 hours. schema: type: string maxLength: 255 schemas: CustomField: type: object description: > A user-defined custom field attached to a parent resource type (`parent_type` is one of: account, product, order, vendor_bill, etc.). Values are stored separately in `entity_custom_field_values` and read/ written via the `/custom_fields/{parent_type}/{parent_id}/values` and `/custom_fields/{custom_field_id}/values/{parent_id}` endpoints. Scope: custom_fields:read / custom_fields:write / custom_fields:delete. properties: id: type: string format: uuid readOnly: true object: type: string example: custom_field entity_id: type: string format: uuid readOnly: true parent_type: type: string description: Parent resource type this field attaches to. 1..30 chars. example: account field_key: type: string description: >- Stable machine identifier. 1..80 chars. Unique per (entity, parent_type). example: tax_id_secondary label: type: string description: Human-readable label rendered in UI. 1..150 chars. example: Secondary Tax ID field_type: type: string enum: - text - number - date - datetime - boolean - json - select - multiselect description: >- Storage type. Drives which `value_*` column is written in entity_custom_field_values. example: text required: type: boolean default: false options: type: array nullable: true items: type: string description: For select / multiselect field_type only. default_value: type: string nullable: true help_text: type: string nullable: true display_order: type: integer default: 0 is_active: type: boolean default: true metadata: type: object description: Free-form caller metadata. Default {}. deleted_at: type: string format: date-time nullable: true readOnly: true description: Set by softDelete; cleared by restore. created_at: type: string format: date-time readOnly: true updated_at: type: string format: date-time readOnly: true 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 responses: Error: description: Error response (400/401/403/404/409/422/429/500) content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' 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. ````