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