I just wanted to update my app, as it seems the in-app purchases were not updated in the first submission.
I created a new build and increased the version number by a minor increment, from 1 to 1.1, to ensure it gets processed. The build appears in TestFlight, but the plus button adjacent to the "Build" subsection does not appear, preventing me from selecting a new version. Please see the attached images.
VERY VERY FRUSTRATING