--- title: "Billabex for developers and agents" description: "The Billabex developer portal: API credentials, a quickstart, the OpenAPI specification, the MCP server, and guides in English and French." canonical: https://developer.billabex.com/developers/ lang: en last-updated: 2026-09-13 --- # Billabex for developers and agents > The Billabex developer portal: API credentials, a quickstart, the OpenAPI specification, the MCP server, and guides in English and French. Source: https://developer.billabex.com/developers/ Language: English (en) Documentation: https://developer.billabex.com/en/ (English), https://developer.billabex.com/fr/ (français) Billabex is an accounts receivable platform: an organization loads its customer accounts and unpaid invoices, and an AI agent conducts the payment follow-ups on its behalf. Everything the product does is available through the REST API, the MCP server, and the web app alike. This page is the entry point to all of it. ## Get API credentials Billabex uses OAuth 2.1 with PKCE. There is no API key to request from a salesperson, and no form to fill in: a client obtains its own credentials in one of two ways. ### Register a client automatically The authorization server supports OAuth 2.0 Dynamic Client Registration and publishes its registration endpoint in its metadata, so a client, an agent included, registers itself without human approval. ```bash curl -s https://next.billabex.com/.well-known/oauth-authorization-server | jq .registration_endpoint ``` ### Create a client by hand Sign in with a Billabex account and manage the OAuth clients of your organization from the OAuth Clients page: name, redirect URIs, scopes, and the client secret, shown once. ## Quickstart The first call takes no credential at all. It returns the OAuth endpoints, both rate-limit quotas, and every documentation URL, which is enough to plan the rest. ### 1. Look at the API before you authenticate The status endpoint is public and rate limited per IP address. Its response carries the RateLimit and RateLimit-Policy headers, so a client can size its throttling before its first authenticated call. ```bash curl -i https://next.billabex.com/api/public/v1/status ``` ### 2. See what the MCP server can do The MCP tool catalogue is public too. It lists every tool with its description, its JSON Schema and the scope it needs. Calling the MCP endpoint itself requires a token. ```bash curl -s https://next.billabex.com/mcp/tools | jq '.tools[].name' ``` ### 3. Authorize Run the OAuth 2.1 authorization code flow with PKCE (S256) and ask only for the scopes the task needs. The scopes guide lists them one by one. ### 4. Make your first authenticated call Almost every endpoint takes an organizationId. Read it once, cache it, then call the rest of the API with it. ```bash curl -s https://next.billabex.com/api/public/v1/organizations \ -H "Authorization: Bearer $BILLABEX_ACCESS_TOKEN" ``` ## Machine-readable contracts Every one of these is readable without a credential, and is the source an agent should prefer over prose. - [OpenAPI specification](https://developer.billabex.com/openapi.json): Typed operations with unique operation ids, OAuth scopes, and the JSON error schema returned on every failure. - [Agent instructions (llms.txt)](https://developer.billabex.com/llms.txt): When to use Billabex, how an agent should call it, and where each resource lives. - [Agent skill](https://developer.billabex.com/.well-known/agent-skills/index.json): The Billabex skill and its discovery index, following the agent-skills well-known convention. - [MCP server manifest](https://developer.billabex.com/mcp-server.json): Registry-compatible metadata for the Streamable HTTP MCP server. - [MCP tool catalogue](https://next.billabex.com/mcp/tools): Every MCP tool with its description, JSON Schema and required scope, served without a token. - [API status and discovery](https://next.billabex.com/api/public/v1/status): The live discovery document of the public API: OAuth endpoints, quotas, documentation URLs. ## Documentation The portal is published in English and in French. The two are translations of one another; read the one you write in. - [English documentation](https://developer.billabex.com/en/): Guides, API reference, and the OAuth clients page, in English. - [Documentation en français](https://developer.billabex.com/fr/): Guides, référence de l'API et page des clients OAuth, en français. - [Getting started](https://developer.billabex.com/en/guides/getting-started/): From an OAuth client to a first authenticated call, step by step. - [OAuth scopes](https://developer.billabex.com/en/guides/scopes/): Every named scope, what it grants, and which one a given endpoint needs. - [Errors](https://developer.billabex.com/en/guides/errors/): The single JSON error shape, its codes, and what each resolution means. - [Rate limiting](https://developer.billabex.com/en/guides/rate-limiting/): Both quotas, the headers that report them, and how a client should throttle itself. ## Environments and test data Billabex does not publish a shared sandbox today. Read that as it is written: the parts of the contract that need no data are open to anyone, and the parts that need data need an organization of your own. What you can exercise with no account at all: the status endpoint, the MCP tool catalogue, the OpenAPI specification, the OAuth metadata documents, and dynamic client registration. That covers discovery, client setup, and the whole shape of the contract. What needs an organization: anything that reads or writes accounts, invoices, credit notes, communications or tasks. Create an organization, keep your test invoices in it, and pause the payment follow-ups on the accounts you use for testing so that no message is ever sent to a real customer. Follow-ups can be paused per account, and an invoice below the minimum amount configured for the organization is never followed up at all. If a dedicated sandbox would change how you integrate, say so when you contact us: it is the kind of thing that gets built when integrators ask for it. ## Support Use the Billabex contact form with the endpoint or MCP tool name, the HTTP status, and an approximate timestamp. Never send access tokens, client secrets, or customer personal data in a support request. [Billabex contact form](https://www.billabex.com/en/contact-us/) --- Billabex developer portal. OpenAPI specification: https://developer.billabex.com/openapi.json. Agent instructions: https://developer.billabex.com/llms.txt. Complete documentation: https://developer.billabex.com/llms-full.txt.