Source: https://billingmart.com/developers/connect

# One server, five ways in

Claude and Claude Code, ChatGPT with a custom connector, Gemini Enterprise, Gemini Business and the Gemini CLI. Each page says which steps we have run against the platform and which we have not.

[API reference](https://billingmart.com/developers/api) [OpenAPI document](https://api.billingmart.com/v1/openapi.json)

Connect an assistant

## The rules, in order

01

## Before you start

Every platform below connects to the same address, `https://api.billingmart.com/mcp`, and signs in with OAuth 2.1 and PKCE. You sign in as yourself, choose the workspace, and tick the access the assistant may have. It can never hold more than your role allows, and anything that sends a message or moves money still waits for a person to approve it.

**What is checked, and what is not.** The server side: the discovery documents, client registration for the hosts below, the consent page and the tool list, is exercised by our own test suite on every change. The menus and button names inside each assistant belong to that product and change without notice. We have not yet walked these pages through on a fresh account for each platform, so every platform step carries a note saying so. These pages were written on 9 October 2026.

02

## Claude (claude.ai)

1. In Claude, open **Settings**, then **Connectors**, and choose **Add custom connector**.
2. Paste `https://api.billingmart.com/mcp` and add it. Claude registers itself with the server on its own.
3. Sign in to BillingMart in the window that opens, choose the workspace and the access, and pick Ask (the default) or Plan.

**Not yet run against the platform.** Claude is on the server’s list of verified hosts, so the consent page shows it as verified. The menu names above are from our setup notes.

03

## Claude Code

Add the server, then sign in Sample

```
claude mcp add --transport http billingmart https://api.billingmart.com/mcp
```

Start Claude Code and use its `/mcp` command to sign in; a browser window opens on the same consent page.

**Not yet run against the platform.** The command is the one Claude Code documents for a remote HTTP server. We have not run it against the current release.

04

## ChatGPT (custom connector)

1. In ChatGPT’s settings, turn on the option that lets you add your own connectors (OpenAI calls it Developer mode; a plan that has it is required).
2. Add a connector, give it the address `https://api.billingmart.com/mcp`, and choose OAuth.
3. Sign in to BillingMart, choose the workspace and the access.

For plain chat, ChatGPT needs two tools named `search` and `fetch`. We provide both: `search` looks across invoices, estimates and clients and returns titles with links, and `fetch` returns one record as text with a link to it in the console.

**Not yet run against the platform.** ChatGPT’s hosts are on the verified list. Where the custom-connector option sits in the settings, what OpenAI calls it, and which plans have it are OpenAI’s to say and may differ from this page.

05

## Gemini Enterprise and Gemini Business

These take a connector added by an administrator, over Streamable HTTP, with a client you registered ahead of time rather than one the assistant creates for itself. A workspace owner or admin registers that client for the workspace; it is a confidential client bound to that one workspace, its secret is shown once, and consent for any other workspace is refused.

1. As a BillingMart owner or admin, register a client for the workspace and keep the id and secret.
2. As the Gemini administrator, add a custom MCP connector with `https://api.billingmart.com/mcp`, the client id and the client secret.
3. Each person then signs in to BillingMart from Gemini and chooses their access.

**Not yet run against the platform.** We have not run this against a Gemini Enterprise tenant, nor a Gemini Business one. Where the owner registers the client in the console, and the names of the fields on Google’s side, are unconfirmed.

06

## Gemini CLI

The Gemini CLI can read a remote server from its settings file and discover the sign-in itself, or take a token you already hold.

settings.json Sample

```
{
  "mcpServers": {
    "billingmart": { "httpUrl": "https://api.billingmart.com/mcp" }
  }
}
```

**Not yet run against the platform.** This follows the Gemini CLI’s documented shape for a remote server; we have not run it, and the sign-in step is unconfirmed.

07

## The consumer Gemini app

We make no claim about the consumer Gemini app, either way. This page will say more when we have checked.

08

## After you connect

The assistant’s tool list is built from what you ticked, so a read-only connection lists no write tools. You can narrow or remove the connection at any time under Connected apps in the console. The rules for modes, approvals and tenant text are on the [MCP server](https://billingmart.com/developers/mcp) guide.

Next guide

## Webhooks

BillingMart signs every delivery with a secret that is shown to you once and kept sealed on our servers, retries with backoff, and keeps a log of every attempt.

[Continue to Webhooks →](https://billingmart.com/developers/webhooks)

## Try it in your sandbox

A bmk_test_ key reaches only your sandbox workspace.

[Start free](https://app.billingmart.com/sign-up) [All guides](https://billingmart.com/developers)

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This is the Markdown copy of https://billingmart.com/developers/connect. Live plans, prices and limits are published as JSON at https://billingmart.com/plans.json and https://billingmart.com/agent-info.json.