Never once have I had this issue. Google OAuth doesn’t work no matter what I try. Client ID, client secret, callback URI, and everything else are correct. I’ve run this exact setup for months without issue, but now all of a sudden, nothing I do works. Any suggestions?
Would really appreciate help on this, thanks!
Hey there, I hope this can help you. Apparently there was an issue with n8n (several people having the same problem). n8n released version 2.1.4 to resolve this. Go to your n8n Cloud dashboard (Admin Panel) and check if an update is available. Upgrading to 2.1.4 or later should immediately fix the redirect_uri_mismatch error without you needing to change anything in Google Cloud.
n8n was displaying one redirect URL (e.g., https://oauth.n8n.cloud/oauth2/callback) but actually sending a different one (e.g., https://your-instance.app.n8n.cloud/rest/oauth2-credential/callback) to Google.
Hope this solves your issue, fingers crossed!
You’re an actual legend, thank you so much! This fixed it. Literally sat for 2h debugging this yesterday haha
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Wooohooo! Glad it worked @George_Tasan! it can be really frustrating, glad to help out! If you can, please mark my answer to “solve the issue” 
enjoy the peace of overcoming these frustrating blockers