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

# Link documents

> Links sales, purchases, or payrolls; IDs from another business come back in `rejected_ids`.

**Required permission:** `projects.write`



## OpenAPI

````yaml /api-reference/openapi.en.json post /projects/{id}/items
openapi: 3.0.3
info:
  title: FileXpress External API
  version: 1.0.0
  description: >-
    API for integrating third-party systems with FileXpress: billing, HR,
    accounting, inventory, projects, accounts receivable and payable, treasury,
    pricing and promotions, and cash. Current base URL: /api/external/v1. The
    legacy unversioned path (/api/external) will be removed on January 1, 2027;
    migrate to /api/external/v1 (same endpoints, only the base URL changes). The
    v2 API (/api/external/v2) exposes currencies and exchange rates, sales and
    purchases in foreign currency, taxes by id, payrolls with branch, and errors
    with a stable `code`; its operations carry the /v2 prefix in the path. We
    suggest migrating to the available v2 routes before March 30, 2027.
servers:
  - url: https://api.filexpress.app/api/external/v1
    description: Production
security:
  - ApiKey: []
tags:
  - name: General
  - name: Billing · Sales
  - name: Billing · Purchases
  - name: Billing · Customers
  - name: Billing · Suppliers
  - name: Billing · Products
  - name: Catalogs
  - name: HR · Employees
  - name: HR · Attendance
  - name: HR · Labor rules
  - name: HR · Schedules
  - name: HR · Holidays
  - name: HR · Attendance results
  - name: HR · Leave requests
  - name: HR · Payrolls
  - name: Accounting
  - name: Inventory
  - name: Projects
  - name: Accounts receivable
  - name: Accounts payable
  - name: Treasury
  - name: Pricing and promotions
  - name: Cash
  - name: Points of sale
  - name: API v2 · General
  - name: API v2 · Currencies and rates
  - name: API v2 · Countries
  - name: API v2 · Sales
  - name: API v2 · Purchases
  - name: API v2 · Payrolls
paths:
  /projects/{id}/items:
    post:
      tags:
        - Projects
      summary: Link documents
      description: >-
        Links sales, purchases, or payrolls; IDs from another business come back
        in `rejected_ids`.


        **Required permission:** `projects.write`
      parameters:
        - name: id
          in: path
          required: true
          description: Project ID
          schema:
            type: string
            format: uuid
          example: 9d1c5a3e-4b7f-4e2a-9c1d-2f6b8a0e7c11
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ProjectLinkItemsRequest'
            example:
              type: sale
              ids:
                - 9d1c5a3e-4b7f-4e2a-9c1d-2f6b8a0e7c11
                - 3b8e2f10-7c4d-4a9e-b1f2-5d6c7e8f9a01
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                type: object
                required:
                  - status
                  - data
                properties:
                  status:
                    type: boolean
                    example: true
                  data:
                    type: object
                    properties:
                      linked:
                        type: integer
                        description: Documents linked.
                      rejected_ids:
                        type: array
                        items:
                          type: string
                      summary:
                        $ref: '#/components/schemas/ProjectSummary'
                    required:
                      - linked
                      - rejected_ids
                      - summary
              example:
                status: true
                data:
                  linked: 2
                  rejected_ids:
                    - 3b8e2f10-7c4d-4a9e-b1f2-5d6c7e8f9a01
                  summary:
                    total_sales: 12000
                    total_expenses: 6500
                    total_payroll: 2100
                    total_work_orders: 400
                    total_costs: 9000
                    profit: 3000
                    margin_percent: 25
                    budget: 25000
                    budget_used_percent: 36
                    counts:
                      sales: 3
                      expenses: 8
                      payrolls: 2
                      work_orders: 1
        '401':
          $ref: '#/components/responses/E401'
        '403':
          $ref: '#/components/responses/E403'
        '404':
          description: Not found or belongs to another business
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
              example:
                status: false
                message: Project not found
        '422':
          description: Validation error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
              example:
                status: false
                message: Validation errors
                errors:
                  type:
                    - The selected type is invalid.
        '429':
          $ref: '#/components/responses/E429'
components:
  schemas:
    ProjectLinkItemsRequest:
      type: object
      properties:
        type:
          type: string
          description: Document type.
          enum:
            - sale
            - expense
            - payroll
        ids:
          type: array
          minItems: 1
          maxItems: 500
          items:
            type: string
            format: uuid
      required:
        - type
        - ids
    ProjectSummary:
      type: object
      properties:
        total_sales:
          type: number
        total_expenses:
          type: number
        total_payroll:
          type: number
        total_work_orders:
          type: number
        total_costs:
          type: number
        profit:
          type: number
        margin_percent:
          type: number
          nullable: true
        budget:
          type: number
          nullable: true
        budget_used_percent:
          type: number
          nullable: true
        counts:
          type: object
          properties:
            sales:
              type: integer
            expenses:
              type: integer
            payrolls:
              type: integer
            work_orders:
              type: integer
    Error:
      type: object
      properties:
        status:
          type: boolean
          example: false
        message:
          type: string
        errors:
          type: object
          additionalProperties:
            type: array
            items:
              type: string
          description: Errors per field (validation only).
      required:
        - status
        - message
  responses:
    E401:
      description: Missing or invalid API Key
      content:
        application/json:
          example:
            status: false
            message: Invalid API Key.
    E403:
      description: Integration without the required permission or deactivated
      content:
        application/json:
          example:
            status: false
            message: This integration does not have the 'hr.employees' permission.
            required_scope: hr.employees
    E429:
      description: Rate limit exceeded
      content:
        application/json:
          example:
            status: false
            message: Rate limit exceeded. Please try again later.
            rate_limit: 100
  securitySchemes:
    ApiKey:
      type: apiKey
      in: header
      name: X-API-Key
      description: Integration API Key (Integrations → New Integration).

````

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