I wanted to share a solution that I came across to a problem that I was having with my Galaxy S10. This is my first post here, so forgive me if this has already been addressed. The problem was that when I would attempt to manually select a mobile network from the "Network operators" menu, I would get an error that said "Unable to connect. Try later." I first reached out to Samsung Support on Twitter about this, but they were unable to resolve the issue. I then reached out to TMobile, who is my carrier. They had me replace my SIM card, but this also did not resolve the issue. Doing some tinkering with my phone, I noticed that in the ServiceMode menu, there is an option that says "BLOCK SET BY AP ()." This was selected by default. When I disabled this, I was now able to manually select a mobile network sucessfully, without the error appearing. The exact steps to do this are:
Dial *#2263# from the dialer
Tap "BLOCK SET BY AP ()" so that there is no * inside of the parenthesis
I am making this post because I did extensive research looking for a solution to this problem and was unable to find it anywhere. Even Samsung's own support team could not figure this out. I'm hoping that this will help anyone else that runs into this issue.