Square OAuth Error – Unable to Find Client by client_id

Questions
1

Hello,

I’m developing a booking application for Woods Hole Hostel using Base44 and integrating Square payments through OAuth.

When the hostel owner opens our private authorization link and attempts to connect her Square merchant account, Square displays:

“Unable to find client by that client_id”

We’ve verified that:

  • The Production Application ID matches the ID sent in the OAuth authorization request.

  • The authorization request uses Square’s production OAuth endpoint.

  • The production redirect URL is registered in the Square Developer Dashboard.

  • The application has been published with the updated callback URL.

  • Square Sandbox payments have been tested successfully.

The error occurs before the merchant can approve authorization.

Could someone from Square Developer Support help determine why the production OAuth application isn’t being recognized and what needs to be corrected?

Thank you,
AppForge Studio LLC

3

This error means the client_id in the authorize URL doesn’t match any application in the environment you sent it to. In almost every case, the ID and the endpoint come from different environments. Check that the final URL the owner opens has all of these:

  • Host is https://connect.squareup.com/oauth2/authorize (connect.squareupsandbox.com is the Sandbox host).
  • client_id is the Production Application ID, which starts with sq0idp-. An ID starting with sandbox-sq0idb- won’t resolve in production.
  • No extra whitespace, quotes or encoding around the ID. Base44 env vars and URL builders sometimes add these.
  • session=false, so the owner can pick the right Square account.

If those all check out, reply with the full authorize URL the owner opened, with state removed, and we’ll look into it.