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Spain’s tax and labour administrations do not offer a modern API. Behind every payroll, banking or invoicing product that serves Spanish companies there is a team uploading files to the AEAT, the Sistema RED and the SEPE by hand, and answering their notifications. The Melso API is that team as an API. Your platform sends the facts it already has (payslips, invoices, bank movements, employees). Melso turns them into the returns, settlements and notifications the law requires, a person at the company approves the exact version, and Melso’s professionals file it under the company’s representation. You get the administration’s reference and receipt back.
The Melso API is in a design-partner phase. Each operation in the reference says whether Melso runs it in production today (Live capability) or whether it is a contract we are building with design partners (Preview). See Availability.

HR and payroll platforms

Altas and bajas, Social Security settlements, Contrat@, Certific@2, modelos 111 and 190.

Business banking

Tax set-aside, receipt capture, reconciliation and quarterly returns for your business customers.

ERPs and invoicing software

VERI*FACTU invoicing, books, VAT returns and corporate tax from the data you already hold.

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How it works

1

Add the company

Create the company on your partner account and complete its fiscal profile, or send the company’s owner to Melso’s hosted onboarding. See Companies and mandates.
2

Get its mandate

The company’s legal representative signs a mandate that lets Melso’s professionals act before the AEAT, the TGSS or the SEPE for the procedures listed. Nothing is filed without an active mandate.
3

Send what you already have

Invoices, expenses and documents, bank movements, employees and payroll runs. Melso categorizes, reconciles and keeps the books.
4

Melso calculates

Returns, settlements and notifications are calculated as the data arrives, with their deadlines in the company’s tax calendar. You are told by webhook.
5

A person approves the exact version

The company’s owner approves through Melso’s approval page, or inside your product under a partner agreement. A changed version needs a new approval. See Approvals and filing.
6

Melso's professionals file

They file under the mandate and record the administration’s reference and receipt, which you read from the API and receive by webhook.

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What it covers

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Three rules the API keeps

  1. Preparation is not approval. Melso and your platform prepare. Only a person at the company approves an invoice or a return, at an exact version.
  2. Approval is not filing. Melso’s professionals file an approved return under the company’s mandate. A calculated return, an approval or an AEAT import file is not a filing.
  3. Only the administration’s receipt proves a filing. A filed return carries the administration’s reference, its CSV and the receipt.

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Become a design partner

Design partners shape the preview contracts, get a test environment with test companies, and go live module by module. Write to hello@melso.ai with the module you need first and the number of companies you serve.

Quickstart

From a company to its first calculated return.

API reference

Every operation with its fields and availability.