> ## Documentation Index > Fetch the complete documentation index at: https://docs.prophia.com/llms.txt > Use this file to discover all available pages before exploring further. # CREATE Custom Field Assignment > Sets the field's value on each of the given Buildings, up to 200 per request. **Required capabilities:** `WRITE:CUSTOM_FIELD` ## OpenAPI ````yaml /api-reference/openapi.json post /rest/v2/accounts/{accountId}/custom-fields/{fieldId}/assignments openapi: 3.1.0 info: title: Prophia API Documentation license: name: Apache 2.0 url: http://springdoc.org version: v2.495.0 servers: - url: https://api.prophia.com description: Prophia API security: - apiKey: [] tags: - name: Accounts description: >- Accounts are the top-level scope for everything in the API. Start here: list your accounts to find the `accountId` every other path requires. - name: Properties description: >- Properties group one or more buildings under a single asset within an account. - name: Buildings description: Buildings are the physical structures where leases and spaces live. - name: Building Spaces description: >- Building spaces are the units inside a building — suites, floors, storage. A space's `suiteNumber` is the canonical name that tag `applicableSpaces` entries reference by string match. - name: Leases description: >- Leases are the agreements occupying building spaces. Each lease carries its source documents and the tags (structured terms) extracted from them. - name: Documents description: >- Documents are the source files attached to leases — original leases, amendments, memorandums, etc. - name: Tags description: >- Tags are the structured lease terms Prophia extracts from documents — a rent amount, a renewal option, a key date — each cited to its location in the source document. STANDARD tags carry a typed `value`; COMPLEX tags carry option details in `tagComponents`. - name: Custom Terms description: >- Custom terms are account-level definitions of extra lease terms your team tracks beyond Prophia's standard set. Tags created from them are ordinary tags with `isCustomTag: true` — the definition and its tag instances are separate resources. - name: Custom Fields description: >- Custom Fields are Account-level fields your team tracks on Buildings beyond Prophia's standard set. A `SINGLE` field holds free text per Building; a `MULTI` field holds one of a fixed list of options. Assignments set a field's value on a Building. - name: Loans description: >- Loans are the financing agreements secured by an account's buildings. Each loan carries its source documents and the terms read from them: summary terms, covenants and reporting deliverables. Loans is a Labs feature in beta, and its endpoints may change. x-beta: true paths: /rest/v2/accounts/{accountId}/custom-fields/{fieldId}/assignments: post: tags: - Custom Fields summary: CREATE Custom Field Assignment description: >- Sets the field's value on each of the given Buildings, up to 200 per request. **Required capabilities:** `WRITE:CUSTOM_FIELD` operationId: assignCustomField parameters: - name: accountId in: path required: true schema: type: string - name: fieldId in: path required: true schema: type: string requestBody: content: application/json: schema: $ref: '#/components/schemas/V2AssignCustomFieldRequest' required: true responses: '200': description: OK content: '*/*': schema: type: array items: $ref: '#/components/schemas/V2CustomFieldAssignmentModel' '400': description: Invalid input — request body failed validation or business rules content: application/json: schema: $ref: '#/components/schemas/V2ErrorResponse' example: error: Invalid Input errorCode: InvalidInput message: dba cannot be blank status: 400 BAD_REQUEST timestamp: '2026-09-02T20:41:03.118Z' localizedMessage: dba cannot be blank '401': description: >- The credential was rejected before the request reached the endpoint — for example a JWT was presented where an API key is required. Only `error` is populated on this path content: application/json: schema: $ref: '#/components/schemas/V2ErrorResponse' example: error: JWT authentication is not supported. Use an API key. '403': description: >- The API key is valid but lacks a required capability or role, the account does not have the REST write module enabled, or the key's building permissions do not cover the requested resource. The message names the missing capabilities only in the first case content: application/json: schema: $ref: '#/components/schemas/V2ErrorResponse' example: error: Access Denied errorCode: AccessDenied message: 'Not authorized. Missing capabilities: WRITE:DOCUMENT' status: 403 FORBIDDEN timestamp: '2026-09-02T20:41:03.118Z' localizedMessage: 'Not authorized. Missing capabilities: WRITE:DOCUMENT' '404': description: No such resource is visible to the account named in the path content: application/json: schema: $ref: '#/components/schemas/V2ErrorResponse' example: error: Entity Not Found errorCode: EntityNotFound message: This entity is not found in the system. status: 404 NOT_FOUND timestamp: '2026-09-02T20:41:03.118Z' localizedMessage: This entity is not found in the system. components: schemas: V2AssignCustomFieldRequest: type: object description: >- Sets a Building Custom Field's value on one or more Buildings. Send `value` for a `SINGLE` field or `optionId` for a `MULTI` field — exactly one of the two. A Building that already has a value for the field is overwritten. properties: buildingIds: type: array description: >- IDs of the Account's Buildings to set the value on; at most 200 per request. items: type: string maxItems: 200 minItems: 0 optionId: type: string description: 'For a `MULTI` field: the ID of one of the field''s options.' value: type: string description: >- For a `SINGLE` field: the free-text value. Reuses the field's existing value that matches ignoring case, if there is one. required: - buildingIds V2CustomFieldAssignmentModel: type: object description: A Building's value for a Building Custom Field. properties: id: type: string description: Prophia internal Custom Field Assignment ID (UUID). readOnly: true fieldId: type: string description: The Custom Field the value is for. readOnly: true buildingId: type: string description: The Building the value is set on. readOnly: true optionId: type: string description: The option holding the value. readOnly: true value: type: string description: The Building's value for the field. readOnly: true createdAt: type: string format: date-time description: When the value was first set on the Building. readOnly: true updatedAt: type: string format: date-time description: When the value was last modified. readOnly: true V2ErrorResponse: type: object properties: error: type: string description: Stable error category example: Invalid Input errorCode: type: string description: Stable error code suitable for programmatic handling example: InvalidInput message: type: string description: Human-readable detail; may aggregate multiple field errors status: type: string description: >- HTTP status of the response as code and reason phrase, matching the response's own status line example: 404 NOT_FOUND timestamp: type: string format: date-time description: When the error was produced, as an ISO-8601 UTC instant example: '2026-09-02T20:41:03.118Z' localizedMessage: type: string description: >- Same text as `message`; present because the body is a serialized exception. Prefer `message` securitySchemes: apiKey: type: apiKey description: >- Prophia API key — either an account key (grants admin level permissions) or a user key with the REST scope. Send it in the `X-API-Key` header, or equivalently as `Authorization: Bearer `. JWTs are rejected on /rest endpoints with 401. name: X-API-Key in: header ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.