is not a valid dart package name
This is documented on the name section of Pubspec Format documentation.
It should be all lowercase, with underscores to separate words, just_like_this. Stick with basic Latin letters and Arabic digits: [a-z0-9_] and ensure that it’s a valid Dart identifier (i.e. doesn’t start with digits and isn’t a reserved word).
Try to pick a name that is clear, terse, and not already in use.