Hi! Service API uses it's own initialization module that is in the package and is routed with attribute routing. I've had similar issues with Service API before, suddenly some routes didn't work while most of them did. So far I have solved it by clearing all temporary IIS and ASP.NET files and updating EPiServer with NuGet. I've never understood the reason for the issue...
If you are hosting in IIS Express -> may be some issues as well. Just discovered. Moved to IIS with no code changes -> all routes registered.
As others have said it uses attribute routing. It also requires atleast 4.5.1 but have seen issues with that so recommend you are running 4.5.2 since Microsoft recommends that as well. One last thing make sure you have a permission in permission to functions for the serviceapi and the user you are using for request has the correct role. You will receive 404's if the permissions are not correct
I've installed the Service API, but any call to anything down the "/episerverapi" path returns a 404. I've been up and down the install instructions mutiple times, and everything is installed and configured (SSL too).
I'm curious how this could work, since I didn't set that routing anywhere. What is the mechanism that routes "/episerverapi" to the Service API in the first place? I've searched my entire project for the string "episerverapi," and it doesn't appear, which tells me the package install didn't set it anywhere.