I got the error message below once; I retried the upload and it went away. If anyone get this you can try doing the same thing to see if it works. Error message '' is not a valid id for the relationship 'build' (ID: 6a679cdd-6ac8-4e16-a164-f4bec1d422fd)

@roopashastri you have to visit your account and agree to changes in the license agreement, check the warning image below. -> https://appstoreconnect.apple.com/