whenever I try to generate a build in EXPO it gives this error:
Build failed: Gradle build failed with unknown error. See logs for the “Run gradlew” phase for more information.
Well, do what the error says and ‘see logs for the “Run gradlew” phase’.
Whatever that means exactly you have to probably ask some EXPO community, I don’t even know what EXPO is besides an exhibition.
Once you found the place to look at and there find something Gradle related you need help with, feel free to come back to this forum. 
I am also facing an issue after updating my expo version from 48 to 49.
I can’t get the solution if any one has then please help me for resolve that issue.
Did you follow my advice?