Use Nefin in Gemini

• The Gemini app or Gemini Enterprise. Google offers custom apps in the Gemini app in some places and accounts only. See Google’s custom apps help. In Gemini Enterprise a team admin adds the server.
• A Nefin account with two-step verification. If you haven’t set it up, Nefin walks you through it the first time you connect.
• AI switched on for at least one company. An owner turns it on in Settings → Company. Gemini can only reach companies where AI is on.
• The Professional or Business plan in Nefin. Starter companies show up as locked, with an upgrade link.

https://api-books.nefin.app/mcp

If the screen asks for a client ID and secret, see the Advanced section.

An admin adds Nefin once. Each member then signs in with their own Nefin login, so everyone keeps their own permissions and the audit log shows who did what.

https://api-books.nefin.app/mcp

https://api-books.nefin.app/oauth/authorize

https://api-books.nefin.app/oauth/token

nefin:read nefin:write

Gemini Enterprise, and some Gemini app setups, cannot register themselves and ask for a client ID and secret instead. Nefin gives you both from one call. You need the redirect URI the console shows. For Gemini Enterprise it is:

https://vertexaisearch.cloud.google.com/oauth-redirect

Run this in a terminal. Put the console’s redirect URI in the command:

curl -X POST https://api-books.nefin.app/oauth/register \
  -H "Content-Type: application/json" \
  -d '{
    "client_name": "Gemini Enterprise",
    "redirect_uris": ["https://vertexaisearch.cloud.google.com/oauth-redirect"],
    "token_endpoint_auth_method": "client_secret_post"
  }'

Nefin answers with JSON. Paste client_id and client_secret into the console’s client ID and client secret fields. The secret is shown once, so copy it right away.

Make sure Nefin is switched on for the chat. In the Gemini app you can type @ to choose which connected app Gemini should use. Then just ask:

• “List my Nefin companies.”
• “Which invoices in Acme Ltd are overdue, and who owes the most?”
• “In Acme Ltd, run the profit and loss for last quarter and compare it with the quarter before.”
• “In Acme Ltd, draft an invoice for Bardhi SHPK: 10 hours of consulting at 45.00, standard VAT.”
• “In Acme Ltd, show me every bill from Bardhi SHPK this year and the total we paid.”
• “Get Nefin's guide for bank statements, then reconcile this statement for Acme Ltd.”
• “Get Nefin's guide for payroll, then show me last month's payroll run in Acme Ltd.”

Amounts come back as exact decimals, so nothing gets rounded along the way.

Nefin gives Gemini 26 tools. Each one works in one company at a time, so name the company in your request. With one company Gemini uses it automatically. With several, Gemini asks which one you mean.

• Read-only by default. The consent screen has an Allow changes switch that starts off. Leave it off and Gemini can look things up and run reports but cannot create or change anything.
• Your permissions, nothing more. Gemini works as you in each company. If your role can’t post journals, neither can Gemini.
• Everything is on the record. Changes appear in the audit log under your name.
• Check before you approve. Read what Gemini proposes before you let it change your books, especially the tools that post, correct or delete: update_document, delete_document, activate_document, record_payment, manage_journal, reconcile_bank_lines, mark_bank_period_reconciled and run_payroll.

To cut off access, go to Account → AI connectors in Nefin and click Disconnect next to Gemini. It takes effect immediately. To remove Nefin from Gemini as well, delete the custom app in Gemini’s settings.

Every AI app has its own limits. This table shows what each one means for Nefin and what to do about it. The app on this page is first.

I can't find the custom app option in the Gemini app

Google offers custom apps in the Gemini app only in some places and accounts. It needs a personal Google account, an adult user in the United States, and Keep Activity switched on. Work and school accounts don't have it. Gemini Enterprise has its own setup, described above.

The console asks for a client ID and secret

Some Gemini setups can't register themselves with a server. Register a client with the command in the Advanced section, then paste the client_id and client_secret it returns.

Registration says the redirect URI is not valid

Nefin accepts https redirect URIs only, and the register call must include the exact redirect URI the console shows. Copy it from the console again. The client name may not contain the word Nefin.

Sign-in fails after I approve

The client secret or redirect URI doesn't match what you registered, or the console isn't sending the sign-in code with PKCE. In Gemini Enterprise switch on PKCE support and paste the exact values from the registration answer.

The Nefin sign-in page says AI features are not enabled

None of your companies has AI switched on. Ask an owner to turn it on in Settings, Company, then connect again.

Gemini can't find a company

Gemini only sees companies where AI is on and where you are an active member. Ask it to list your Nefin companies to see exactly what it can reach.

Gemini asked which company to use

You belong to more than one company, so Gemini asks before it does anything. Name one, for example "in Acme Ltd, ...". With only one company Gemini picks it for you.

Gemini doesn't see a tool or uses an old tool name

Disconnect and reconnect Nefin in the app's settings so Gemini reads the tool list again, then start a new chat.

A change was refused

The connection is read-only unless you turned on Allow changes when you connected. To change that, disconnect Nefin under Account, AI connectors, and connect again with Allow changes on. Your role in the company must also allow the action.