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"qualifier" is a newly created Claim. "claim" is an existing Claim of an item, which is received with item.claims.

>>> claim.addQualifier(qualifier)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "core/pywikibot/page.py", line 3017, in addQualifier
    data = self.repo.editQualifier(self, qualifier, **kwargs)
  File "core/pywikibot/site.py", line 721, in callee
    return fn(self, *args, **kwargs)
  File "core/pywikibot/site.py", line 3882, in editQualifier
    data = req.submit()
  File "core/pywikibot/data/api.py", line 401, in submit
    raise APIError(code, info, **result["error"])
pywikibot.data.api.APIError: no-such-qualifier: Claim does not have a qualifier with the given hash

The used code worked once.