> ## Documentation Index > Fetch the complete documentation index at: https://docs.flowpayroll.ai/llms.txt > Use this file to discover all available pages before exploring further. # Add a former employee to an open pay run > Adds someone who has already left to an open pay run so they can be paid after leaving, for example a late commission or service charge. Former employees are excluded from the payroll-config roster once their leaving date reaches a finalised payslip, so they cannot be picked up by a pay run any other way. Where the P45 has already been issued, the resulting payslip is taxed at 0T on a week 1 / month 1 basis and reported on the next FPS with the payment-after-leaving indicator, the original leaving date and the original payroll ID. No second P45 is issued. ## OpenAPI ````yaml /api-reference/specs/pay-api.yaml post /payroll/{payrollConfigId}/{year}/{period}/employees openapi: 3.0.3 info: title: FlowPayroll API description: >- API for payroll management, including payroll upload, lock, HMRC submission, employee management version: 0.1.0 servers: - url: https://api.sandbox.flowpayroll.ai/v1 security: - XAuthToken: [] XOrgId: [] tags: - name: Employees description: >- Create, retrieve, update, and delete employee records, and look them up by NI number or payroll ID. - name: Starters & leavers description: Set and clear starter and leaver details, individually or in bulk. - name: Tax codes description: >- Manage employee tax codes and query the effective tax code and NI category on a given date. - name: NI & identifiers description: Manage NI categories, National Insurance numbers, and payroll IDs. - name: Student loans description: Start and end student and postgraduate loans. - name: Payroll setup description: Assign an employee's payroll config and set opening balances. - name: Payroll - name: Payroll lines - name: PayrollConfig - name: Pay Elements - name: Calculator - name: Payslip - name: RTI - name: YearEnd - name: Organisation paths: /payroll/{payrollConfigId}/{year}/{period}/employees: post: tags: - Payroll summary: Add a former employee to an open pay run description: >- Adds someone who has already left to an open pay run so they can be paid after leaving, for example a late commission or service charge. Former employees are excluded from the payroll-config roster once their leaving date reaches a finalised payslip, so they cannot be picked up by a pay run any other way. Where the P45 has already been issued, the resulting payslip is taxed at 0T on a week 1 / month 1 basis and reported on the next FPS with the payment-after-leaving indicator, the original leaving date and the original payroll ID. No second P45 is issued. operationId: AddEmployeeToPayrollRun parameters: - name: payrollConfigId in: path required: true schema: type: string description: The ID of the payroll configuration - name: year in: path required: true schema: type: integer example: 2026 description: The year in format yyyy - name: period in: path required: true schema: type: string example: '1' description: The period in format mm requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/AddEmployeeToPayrollRunDto' responses: '200': description: >- The former employee was added to the pay run, or was already on it. Their payslip is generated asynchronously. content: application/json: schema: $ref: '#/components/schemas/ResponseBody' '400': description: Invalid request, or the person is still employed content: application/json: schema: $ref: '#/components/schemas/ResponseBody' '404': description: Payroll config, pay run or employee not found content: application/json: schema: $ref: '#/components/schemas/ResponseBody' '409': description: The pay run is no longer open content: application/json: schema: $ref: '#/components/schemas/ResponseBody' '500': description: An error occurred content: application/json: schema: $ref: '#/components/schemas/ResponseBody' components: schemas: AddEmployeeToPayrollRunDto: type: object properties: employeeId: type: string description: The ID of the former employee to add to the pay run example: employee-001 required: - employeeId ResponseBody: type: object properties: message: $ref: '#/components/schemas/MessageWithTokenResponse' content: type: object properties: data: type: object nullable: true metadata: type: object nullable: true properties: dateFormat: type: string default: yyyy-MM-dd dateTimeFormat: type: string default: yyyy-MM-ddTHH:mm:ss.fffZ paginationToken: type: string nullable: true validationIssues: type: array items: $ref: '#/components/schemas/ValidationIssue' messageToken: type: string MessageWithTokenResponse: type: object properties: text: type: string token: type: string tokenArguments: type: array items: $ref: '#/components/schemas/ValidationIssueArgument' ValidationIssue: type: object description: > Field validation item. `reasonToken` is a stable snake_case key for i18n or custom client messages; `reason` is the default English text from the API. properties: field: type: string description: Dot-path of the field (e.g. name.firstName, address.line1). reason: type: string description: Default human-readable message. reasonToken: type: string description: Machine-readable error identifier (snake_case). reasonTokenArguments: type: array nullable: true items: $ref: '#/components/schemas/ValidationIssueArgument' ValidationIssueArgument: type: object properties: name: type: string value: type: string securitySchemes: XAuthToken: type: apiKey in: header name: X-Auth-Token description: Access token obtained from OAuth2 client credentials flow XOrgId: type: apiKey in: header name: X-Org-Id description: >- Organisation to scope the request to. Required when the principal can access more than one organisation; optional for single-organisation principals (the authorizer resolves it automatically). ````