How to debug failing kubectl calls?
You said you tried curl 127.0.0.1:8080/api, but regarding to the logs it tries to connect via https. So you should try curl https://127.0.0.1:8080/api.
I searched the source code for the term Service Unavailable and it for example the error description for a HTTP 503 return code.
Out of my guts, I assume you will get an HTTP 503, when you try to curl https://127.0.0.1:8080/api.
Edit: Since you use minikube, we can assume that this is running correctly. In this case it is more likely that there is a configuration issue. Your logs say that kubectl tries to connect to localhost. AFAIK this is the default host. When you start minikube it doesn't run on the host, rather than in a virtual machine. Therefore localhost looks wrong and you should take a look at the kube config.