Connect ChatGPT
Add Invoia to ChatGPT as a custom MCP connector in developer mode.
ChatGPT reaches a remote MCP server through a custom connector, which lives behind developer mode. It is the fussiest of the four clients to set up and the only one where an admin may have to act before you can start.
Check your plan first
Full MCP connectors and developer mode are a beta, offered on ChatGPT Business and Enterprise/Edu workspaces, on the web. Availability moves — OpenAI's developer mode article is the current word.
1. Turn on developer mode
For yourself, in Settings → Security and login, turn on Developer mode.
On a Business or Enterprise workspace an owner has to allow it first, under Workspace settings → Permissions & roles → Connected data → Developer mode / Create custom MCP connectors. Until they do, the toggle is not there to find.
2. Add the server
In the apps and connectors settings, use the + button to create a developer-mode app, and give it:
- URL —
https://invoia.io/api/mcp, including the/mcppath - Authentication — OAuth
https://invoia.io/api/mcpChatGPT registers itself and sends you to an invoia.io sign-in and consent screen. Approve the scopes you want it to have. The new app appears under Drafts until you publish it to the workspace.
3. Use it
Enable the connector for a conversation, then ask in plain language:
Using Invoia, show me every draft invoice older than 30 days.You get the ones you are assigned to, and the answer says so — reads default to your own work, and widening to the whole account is explicit and admin-only (Auth and scopes).
Its details page lists the tools it pulled from the server, with a toggle each. If you change what you granted, use Refresh there — ChatGPT caches the tool list, its descriptions and the server instructions, and will otherwise keep offering tools your new token no longer carries.
What to expect on writes
ChatGPT gets the same propose → commit contract as every other client: a
plan_* tool returns a written plan, and nothing changes until commit
runs on your say-so. See
The propose → commit contract.
Deep research cannot use this connector
Deep research and company-knowledge lookups only call a connector's
search and fetch tools. Invoia implements neither: its read tools
are typed queries against your books, not a document index, and
pretending otherwise would hand a research run a licence to roam. Use
a normal chat when you want Invoia to answer or propose a change.
Troubleshooting
- No developer mode toggle — the workspace has not enabled it. Only an owner can, in workspace settings.
- "Failed to connect" — check the URL ends in
/mcp. The basehttps://invoia.iois the OAuth issuer, not the MCP endpoint, and will not answer a tool call. - Tools you granted are missing, or removed ones linger — hit Refresh on the app's details page. The catalogue is built from your token's scopes at connect time and ChatGPT caches it.
- It answers from memory instead of calling a tool — name the connector in the message ("using Invoia") and confirm it is enabled for that conversation.
- A write did not happen — a plan is not a commit. Confirm the plan explicitly; if the conversation moved on, proposals expire after fifteen minutes and the tool has to be re-run.