Hi Alexandru! I suggest you enable Salsa CI for the repository. It will immediately reveal a couple of errors you have, and give you feedback when they are fixed. Here is an example of Salsa CI enabled in a Python package: https://salsa.debian.org/python-team/packages/rdiff-backup/-/blob/debian/latest/debian/salsa-ci.yml
You also got some advice about using DEP14 branch names. If you adopt a gbp.conf like in https://salsa.debian.org/python-team/packages/rdiff-backup/-/blob/debian/latest/debian/gbp.conf all those branch names and other things will be automatic after initial configuration, so you won't need to pass them manually to git-buildpackage. Third file you might want to check out is https://salsa.debian.org/python-team/packages/rdiff-backup/-/blob/debian/latest/debian/README.source.md for reference on what commands exactly to use in typical package lifecycle.
