OAuth 2.0 – App Fails to Connect: "Uh oh, there's a connection problem" Error After Redirect

Hi Intuit ,

I'm integrating QuickBooks OAuth 2.0 with my app "Pay-History", and I'm encountering a persistent issue at the final step of the authorization flow.

After the user authorizes access, instead of being redirected properly, they are shown this error:

"Uh oh, there's a connection problem. Sorry, but Pay-History didn’t connect."

Here’s what I’ve checked so far:

• I’ve listed the redirect_uri exactly as:

   

  https://developer.intuit.com/v2/OAuth2Playground/RedirectUrl

  in the Keys & Credentials → Settings → Redirect URIs section.

• I’m using development credentials (client_id and client_secret) for a sandbox app.

• I’m using a fresh authorization code each time.

• I’ve confirmed the redirect_uri used in both the authorization URL and the token POST request are identical and URL-encoded properly.

• My app is using the correct OAuth scopes.

Additional Info:

• App Name: Pay-History

• Environment: Development

• Redirect URI: https://developer.intuit.com/v2/OAuth2Playground/RedirectUrl

• Error Screenshot

Can anyone help me figure out why this connection error occurs even though everything appears to be configured properly?

Thanks in advance