I am working on ZOHO Desk automation and need to get the ZOHO auth token for n8n

I have created the app in ZOHO Desk API, got client id and client secret. Added all data required to get a token in n8n.

After I sign in with my ZOHO credentials in ZOHO oauth2 login window and accepting the grant operation, I get the page with the address https://aitautomate.app.n8n.cloud/rest/oauth2-credential/callback (and long list of parameters) and text

"Error: Unsupported content type: text/html;charset=utf-8

More details

Failed to connect. The window can be closed now." 

I tried to construct the token request URL and use it in browser, and I got the text

"Something went wrong. Please try again!"

What could be the reason? How can I get more info about the error?