If you create a SemVer attribute in the dictionary, you should write:

1.0.1,2.0.2,3.0.3

And if you don't give a correct SemVer, the parser will fail and notify you to correct it. But if you this

1.0.1, 2.0.2, 3.0.3

And include a space before each version, there is no parsing helpful error about your problem. The submit button produces a red box that says something went wrong and you must go into the Developer Tools to find a reason.