TFS 2018 Doesn't recognize agent capabilities

Question

TFS 2018 build won't run because it says it can't find an agent with the needed capabilities even though I have an agent setup with all the necessary capabilities.

Answer 1

It was because I was creating a custom capability but didn't save it correctly. All I needed was a capability called Xamarin.Android so I created this custom capability but when I created it, I didn't know I also had to set a value for it before the Save Changes button will become clickable. After I put in a dummy value for Xamarin.Android it let me save changes and then the build worked.