OAuth2 Redirect URL returns 404 not found

[lohart13]

I have setup a custom connector that using OAuth2 authentication however I'm having issues trying to get this to authenticate on app.powerbi.com via a personal or enterprise gateway.

The connector successfully authenticates when using it with Power Bi desktop however as soon as I publish the report and try to setup authentication for the dataset, I get a 404 not found error returned as below.

The code returned by the OAuth2 service is quite long, between 4000-5000 characters. Is there a query or URL length limit for the redirect_uri https://oauth.powerbi.com/views/oauthredirect.html?

I did some testing with my own OAuth2 server and as soon as the authorization code exceeded about 4200 characters, I started getting the same issue.