Xero api Integration., Sample oauth2 app works on localhost but cannot find way to make it work in production

Question

See https://github.com/XeroAPI/xero-netstandard-oauth2-app

I simply want to get this sample app up and running on the webserver. Works perfectly on localhost but I must be doing something wrong as it never authenticates on production server.

I believe the only change I need to make is the CallbackUri in appsettings.json

here is that file (devel environment is commented out)

I update my xero app settings CallbackUri including the final forward slash.

Would greatly appreciate any advice on this.

Have repeatedly created and destroyed xero apps to test with a clean app.

The domain is actually a subdomain if that makes any difference. has a paid for, working standard ssl

Here is the error I get on the webserver.

enter image description here

Similar problem to https://stackoverflow.com/questions/74870821/asp-net-core-web-api-my-api-works-on-localhost-but-not-on-my-plesk-webserver

Publishing is done using VS2022

I have this feeling that it did actually work once (in production) and I have a memory of an error something to do with IIS pool. But I cant be sure. Swapping between devel to prod so many times I am easily confused. But this might actually suggest something if it is true.