When starting the app I received a message about not being able to check for updates and when I tried to install mods I kept getting an exception about not being able to decrypt data. I downloaded the source code and ran it and discovered the issue. Seems to be a TLS version issue. According to my computer's registry, I only have the TLS 1.3 client (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols).

I got everything working by doing either of the following two things:

• Change the target framework from .NET 4.6.2 to 4.7
• Set the ServicePointManager.SecurityProtocol to SecurityProtocolType.Tls12 in Application_Startup
  • ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12

I figured I would create an issue in case anyone else had the same problem.