I think I found (my issue) . There is no need for the plus sign.
First I had to remove my current build from the review, to do that I had to click on the link inside a tip just above the "Version information:
then I could update the build (delete and choose the another build from testflight) and the version label.
After saving I could submit my current build to review.
This way I don't need the plus sign afterall...
EdwardKoetsjarjan
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