> ## Documentation Index > Fetch the complete documentation index at: https://docs.melso.ai/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Melso MCP: https://mcp.melso.ai/mcp (OAuth; one company per connection). Documentation-search MCP: https://docs.melso.ai/mcp; it does not act on customer accounts. > > Use the live tool list and respect company membership. Ask the person to approve the exact invoice or tax return version in the signed-in app. Melso's professionals prepare and file included returns after approval; an AI assistant does not file. A prepared file or an approval is not evidence of filing: only the AEAT's reference and receipt are. Keep credentials out of chat and logs. # Request an alta, baja or variación > Asks Melso to communicate an employee's registration, deregistration or data change to the TGSS through the Sistema RED, under the company's mandate. **Preview.** A contract we are building with design partners. It is not callable yet, and fields can still change. See [Availability](/api/availability). Timing is the law's, not Melso's: an alta must reach the TGSS before the employee starts work, and a baja or a variación within three calendar days of the event. Send the request as soon as your platform knows. ## OpenAPI ````yaml api/openapi.yaml POST /companies/{company_id}/social-security/affiliations openapi: 3.1.0 info: title: Melso API version: 1.0.0-preview summary: Spanish tax and labour compliance for the companies on your platform. description: | The Melso API lets an HR, payroll, banking or ERP platform run the Spanish tax and labour obligations of the companies it serves: invoices, books, tax returns, Social Security and employment notifications. Melso calculates and prepares. A person at the company approves the exact version. Melso's professionals file under the company's representation, and the filing is proven only by the administration's reference and receipt. Every operation states its availability in `x-melso-status`: - `live`: Melso runs this capability in production today. Partner keys reach it once a partner account is enabled. - `preview`: a contract proposed to design partners. Not callable yet. `x-melso-actor: person` marks a decision a signed-in person makes in Melso; a partner sends them the approval link instead. contact: name: Melso partnerships email: hello@melso.ai url: https://docs.melso.ai/api/overview servers: - url: https://api.melso.ai/v1 description: API. Keys and access are issued per partner. security: - partnerKey: [] tags: - name: Companies description: The companies you operate for, their fiscal profile and hosted onboarding. - name: Mandates description: >- The company's representation of Melso before the AEAT, the TGSS and the SEPE. - name: Webhook endpoints description: Where Melso sends signed events about your companies. - name: Invoicing setup description: Registration of the company as a VERI*FACTU or TicketBAI invoice issuer. - name: Customers description: The company's invoice customers. - name: Invoices description: >- Drafts, approval, legal registration, delivery and payment of the company's invoices. - name: Expenses description: >- Purchase invoices and receipts, with their AEAT category and deductibility. - name: Income description: Income invoiced outside Melso. - name: Documents description: >- Files the company gives Melso, and Melso's structured reading of an invoice or receipt. - name: Banking description: >- Bank accounts, movements, statements and reconciliation with invoices and expenses. - name: Accounting description: Journal, imported books and the company's financial statements. - name: Tax calendar description: The forms the company must file, with their periods and deadlines. - name: Tax returns description: The returns Melso calculates, their approval and their filing. - name: Corporate tax description: The year's corporate tax (modelo 200) and its instalments (modelo 202). - name: Tax estimates description: What the company should set aside for taxes, as of today. - name: Cases description: Gestiones, the procedures Melso's professionals carry out for the company. - name: Administration notifications description: Electronic notifications from the administration to the company. - name: Certificates description: >- Official certificates such as being up to date with the AEAT or the Social Security. - name: Employees description: The people the company employs. - name: Payroll runs description: >- The payroll results your platform calculated, for Melso to settle and declare. - name: Social Security description: >- Affiliation (altas, bajas and variaciones) and monthly contribution settlements. - name: Employment notifications description: >- Contrat@ contract notifications and Certific@2 company certificates to the SEPE. paths: /companies/{company_id}/social-security/affiliations: parameters: - $ref: '#/components/parameters/CompanyId' post: tags: - Social Security summary: Request an alta, baja or variación description: | Asks Melso to communicate an employee's registration (`alta`), deregistration (`baja`) or data change (`variacion`) to the TGSS through the Sistema RED, under the company's TGSS mandate. Timing is the law's, not Melso's: an alta must reach the TGSS before the employee starts work, and a baja or a variación within three calendar days of the event. Send the request as soon as your platform knows. operationId: createAffiliation parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/AffiliationInput' example: employee_id: 6a1f0c2e-4b3d-4e5f-8a9b-0c1d2e3f4a5b action: alta effective_date: '2026-11-02' responses: '201': description: The request, `pending` until it reaches the TGSS. content: application/json: schema: $ref: '#/components/schemas/Affiliation' '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '409': $ref: '#/components/responses/Conflict' components: parameters: CompanyId: name: company_id in: path required: true description: >- The company's ID. Every company-scoped call works in exactly this company. schema: type: string format: uuid IdempotencyKey: name: Idempotency-Key in: header description: >- A unique key, such as a UUID, that makes a retried create safe. Reusing a key with a different body is refused. schema: type: string maxLength: 255 schemas: AffiliationInput: type: object required: - employee_id - action - effective_date additionalProperties: false properties: employee_id: type: string format: uuid description: >- The employee, with `tax_id`, `social_security_number` and `employment` filled. action: type: string enum: - alta - baja - variacion effective_date: type: string format: date termination_reason: type: string enum: - end_of_contract - dismissal - objective_dismissal - voluntary_resignation - probation_not_passed - retirement - other description: Required for a `baja`. unused_vacation_days: type: integer minimum: 0 description: >- For a `baja`, the vacation paid and not taken, which extends the contribution period. changes: $ref: '#/components/schemas/EmploymentData' description: For a `variacion`, the new employment data. Affiliation: type: object required: - id - employee_id - action - effective_date - status - created_at properties: id: type: string format: uuid employee_id: type: string format: uuid action: type: string enum: - alta - baja - variacion effective_date: type: string format: date status: type: string enum: - pending - submitted - accepted - rejected submitted_at: type: - string - 'null' format: date-time resolution: oneOf: - $ref: '#/components/schemas/Document' - type: 'null' description: The TGSS's resolution once accepted. rejection_reason: type: - string - 'null' created_at: type: string format: date-time EmploymentData: type: object description: Preview. What the TGSS and the SEPE need about the job. properties: contribution_account: type: string pattern: ^[0-9]{11}$ description: The company's código cuenta de cotización (CCC) for this workplace. contract_type: type: string description: >- The contract key, such as `100` (permanent, full time) or `402` (temporary, full time). working_time_coefficient: type: integer minimum: 1 maximum: 1000 description: Part-time coefficient per thousand. `1000` is full time. contribution_group: type: integer minimum: 1 maximum: 11 description: The grupo de cotización. occupation_code: type: string description: The CNO-11 occupation code. collective_agreement: type: string description: The código de convenio colectivo. Document: type: object properties: id: type: string format: uuid filename: type: string content_type: type: string size_bytes: type: integer url: type: string format: uri description: A short-lived download URL. Error: type: object required: - error properties: error: type: string description: What went wrong, for a person to read. code: type: string description: >- A stable code to branch on, such as `invoicing_not_ready` or `version_conflict`. request_id: type: string description: Quote it when you contact Melso. responses: BadRequest: description: >- The request is malformed or a field is invalid. Unknown fields are refused. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: lines[0].vat_rate must be 21, 10, 4 or 0 code: invalid_invoice request_id: req_01JAB3K9X2 Unauthorized: description: The key is missing, revoked or invalid. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: invalid token code: unauthorized request_id: req_01JAB3K9X2 Conflict: description: >- The object changed or is not in a state that allows this. Read it again and decide. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: The tax return changed or is not ready for approval code: version_conflict request_id: req_01JAB3K9X2 securitySchemes: partnerKey: type: http scheme: bearer description: | Your partner secret key, `mk_live_…` for real companies or `mk_test_…` for test companies. Keep it on your servers. See [Authentication](/api/authentication). ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.