"Unknown Application" Error When Authorizing OAuth App

Authentication
1

Problem

I’m trying to set up OAuth authentication for my FreeAgent account to build an MCP (Model Context Protocol) server for personal use. I’ve created an OAuth app in the FreeAgent Developer Dashboard, but when I try to authorize it, I get an “Unknown Application” error with the message: “We don’t recognise this app. Please get in touch with the author of the application you’re trying to approve.”

What I’ve Tried

1. App Configuration

  • Created OAuth app in Developer Dashboard

  • App name: “Claude”

  • OAuth identifier: p0sIUgWBrTC8Oy5B-6bmA

  • Generated and saved OAuth secret

  • Set “Who may use this app?” to “all users”

2. Multiple Redirect URI Configurations

I’ve tried several different redirect URIs:

  • https://developers.google.com/oauthplayground (got Unknown Application)

  • urn:ietf:wg:oauth:2.0:oob (FreeAgent rejected as invalid URL)

  • http://localhost:8080/callback (got Unknown Application)

3. Authorization URLs Tried

All of these give “Unknown Application” error:

https://api.freeagent.com/v2/approve_app?client_id=p0sIUgWBrTC8Oy5B-6bmA&redirect_uri=https://developers.google.com/oauthplayground&response_type=code

https://api.freeagent.com/v2/approve_app?client_id=p0sIUgWBrTC8Oy5B-6bmA&redirect_uri=urn:ietf:wg:oauth:2.0:oob&response_type=code

https://api.freeagent.com/v2/approve_app?client_id=p0sIUgWBrTC8Oy5B-6bmA&redirect_uri=http://localhost:8080/callback&response_type=code

4. What I’ve Verified

  • I’m logged into my FreeAgent account (production, not sandbox) when attempting authorization

  • The client_id and secret are correct (just regenerated to confirm)

  • The redirect URI in the authorization URL matches what’s configured in the app settings

  • I’m including both client_id and response_type=code parameters as per the API documentation

5. Checked “Approved Applications”

When I go to my FreeAgent account → Connections & Add-ons → Approved Applications, my “Claude” app does NOT appear in the list. Only other apps like Zapier, Slips, etc. are shown.

Questions

  1. Is there an app approval or verification process I’m missing? Do OAuth apps need to be approved by FreeAgent before they can be authorized, even for personal use by the developer?

  2. Are apps created in the Developer Dashboard only meant for public distribution, not personal use? If so, is there a different authentication method (like personal access tokens or developer API keys) for accessing my own account?

  3. Is there something specific about the “Who may use this app?” setting that’s causing the issue? Should it be set differently for personal use?

Context

I’m trying to build an MCP server to access my own FreeAgent data for automation purposes. I’ve successfully used other OAuth apps (like Zapier) with my account, so I know my account supports OAuth integrations.

I’ve read through similar forum posts about “Unknown Application” errors and tried the suggested fixes (correct redirect URIs, including client_id parameter, etc.) but the issue persists.

Any guidance from FreeAgent staff or other developers who have successfully set up OAuth apps would be greatly appreciated!

Thanks, Paul