> ## Documentation Index
> Fetch the complete documentation index at: https://chatbotx.io/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Apply arithmetic/append operations to custom field

> Applies a set of operations to one custom field on the contact, in order. Each operation is one of `set`, `append`, `prepend`, `increase`, `decrease` — `increase`/`decrease` treat the current value as a number (no-op if it is not numeric). Example: `{"operations":[{"customFieldId":"123","operation":"increase","value":"1"}]}` to increment a numeric field.



## OpenAPI

````yaml /api-reference/platform-api.json patch /v1/contacts/{identifier}/custom-fields
openapi: 3.1.1
info:
  title: ChatbotX
  version: 0.0.1
servers:
  - url: https://app.chatbotx.io/api
security:
  - bearerAuth: []
  - developerAccessToken: []
  - tokenInSearchParams: []
paths:
  /v1/contacts/{identifier}/custom-fields:
    patch:
      tags:
        - Contacts
      summary: Apply arithmetic/append operations to custom field
      description: >-
        Applies a set of operations to one custom field on the contact, in
        order. Each operation is one of `set`, `append`, `prepend`, `increase`,
        `decrease` — `increase`/`decrease` treat the current value as a number
        (no-op if it is not numeric). Example:
        `{"operations":[{"customFieldId":"123","operation":"increase","value":"1"}]}`
        to increment a numeric field.
      operationId: contacts.applyCustomFieldOperations
      parameters:
        - name: identifier
          in: path
          required: true
          schema:
            type: string
            minLength: 1
            description: >-
              Contact identifier: the numeric contact id, an email address, or a
              phone number.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              properties:
                operations:
                  type: array
                  minItems: 1
                  maxItems: 20
                  items:
                    type: object
                    properties:
                      customFieldId:
                        type: string
                        pattern: ^\d+$
                        description: >-
                          Custom field id (numeric string). Get it from
                          `customFields.list`.
                      operation:
                        enum:
                          - set
                          - append
                          - prepend
                          - increase
                          - decrease
                        type: string
                        description: >-
                          Operation to apply. `increase`/`decrease` treat the
                          current value as a number and are a no-op if it isn't.
                      value:
                        type: string
                        description: >-
                          Operand: the value to set, append, prepend, or
                          add/subtract.
                    required:
                      - customFieldId
                      - operation
                      - value
                  description: Operations to apply in order, up to 20 per request.
              required:
                - operations
      responses:
        '204':
          description: OK
          content:
            application/json:
              schema:
                anyOf:
                  - {}
                  - not: {}
        '400':
          description: '400'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: businessError
                      status:
                        const: 400
                      message:
                        type: string
                        default: An error occurred while processing your request
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
        '401':
          description: '401'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: UNAUTHORIZED
                      status:
                        const: 401
                      message:
                        type: string
                        default: Authentication required
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: INVALID_CHATBOT_TOKEN
                      status:
                        const: 401
                      message:
                        type: string
                        default: Invalid or missing workspace API token
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
        '403':
          description: '403'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: FORBIDDEN
                      status:
                        const: 403
                      message:
                        type: string
                        default: You do not have permission to perform this action
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: trialExpired
                      status:
                        const: 403
                      message:
                        type: string
                        default: Trial expired
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: macLimitReached
                      status:
                        const: 403
                      message:
                        type: string
                        default: Monthly active contact limit reached
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
        '404':
          description: '404'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: notFound
                      status:
                        const: 404
                      message:
                        type: string
                        default: Resource not found
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
        '422':
          description: '422'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: invalidRequestData
                      status:
                        const: 422
                      message:
                        type: string
                        default: Input validation failed
                      data:
                        type: object
                        properties:
                          issues:
                            type: array
                            items:
                              type: object
                              properties:
                                message:
                                  type: string
                                path:
                                  type: array
                                  items:
                                    anyOf:
                                      - type: string
                                      - type: number
                                      - type: object
                                        properties:
                                          key:
                                            anyOf:
                                              - type: string
                                              - type: number
                                        required:
                                          - key
                                        additionalProperties: {}
                              required:
                                - message
                              additionalProperties: {}
                        required:
                          - issues
                        additionalProperties: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                      - data
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: validation
                      status:
                        const: 422
                      message:
                        type: string
                        default: Validation error
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
        '429':
          description: '429'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: tooManyRequests
                      status:
                        const: 429
                      message:
                        type: string
                        default: Too many requests
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
        '500':
          description: '500'
          content:
            application/json:
              schema:
                oneOf:
                  - type: object
                    properties:
                      defined:
                        const: true
                      code:
                        const: INTERNAL_SERVER_ERROR
                      status:
                        const: 500
                      message:
                        type: string
                        default: An unexpected error occurred
                      data: {}
                    required:
                      - defined
                      - code
                      - status
                      - message
                  - $ref: '#/components/schemas/UndefinedError'
components:
  schemas:
    UndefinedError:
      type: object
      properties:
        defined:
          const: false
        code:
          type: string
        status:
          type: number
        message:
          type: string
        data: {}
      required:
        - defined
        - code
        - status
        - message
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
    developerAccessToken:
      type: http
      scheme: bearer
    tokenInSearchParams:
      type: apiKey
      in: query
      name: token

````