Missing data for required field in Marshmallow 3.10.0

Question

I am new to Marshmallow (3.10.0) and I am lost and need help trying to figure out what causes the following error:

AssertionError: ["Input Error - exten: ['Missing data for required field.']"]

The traceback of the error is the following:

Traceback (most recent call last):
  File "/root/wazo_virtualenv_python37/lib/python3.7/site-packages/nose/case.py", line 198, in runTest
    self.test(*self.arg)
  File "/root/wazo-confd/integration_tests/suite/helpers/wrappers.py", line 81, in decorated
    result = func(*new_args, **kwargs)
  File "/root/wazo-confd/integration_tests/suite/helpers/wrappers.py", line 81, in decorated
    result = func(*new_args, **kwargs)
  File "/root/wazo-confd/integration_tests/suite/base/test_call_filter_surrogate_user.py", line 216, in test_get_surrogates_callfilter_exten_when_disabled
    confd.extensions.features(feature['id']).put({'enabled': False}).assert_updated()
  File "/root/wazo-confd/integration_tests/suite/helpers/client.py", line 272, in assert_updated
    self.assert_status(204)
  File "/root/wazo-confd/integration_tests/suite/helpers/client.py", line 242, in assert_status
    assert_that(self.response.status_code, is_in(statuses), self.response.text)

So it seems that the test function test_get_surrogates_callfilter_exten_when_disabled is failing:

def test_get_surrogates_callfilter_exten_when_disabled(call_filter, user):
    response = confd.extensions.features.get(search="bsfilter")
    feature = response.items[0]
  ---> (line 216 in traceback):  confd.extensions.features(feature['id']).put({'enabled': False}).assert_updated()

    with a.call_filter_surrogate_user(call_filter, user):
        response = confd.callfilters(call_filter['id']).get()

        assert_that(
            response.item,
            has_entries(
                surrogates=has_entries(
                    users=contains(has_entries(exten=None, uuid=user['uuid']))
                )
            ),
        )

    confd.extensions.features(feature['id']).put(
        {'enabled': feature['enabled']}
    ).assert_updated()

the feature_extension schema is defined as the following:

class ExtensionFeatureSchema(BaseSchema):
    id = fields.Integer(dump_only=True)
    exten = fields.String(validate=Regexp(EXTEN_REGEX), required=True)
    context = fields.String(dump_only=True)
    feature = fields.String(attribute='typeval', dump_only=True)
    enabled = fields.Boolean()
    links = ListLink(Link('extensions_features'))

and the put function:

def put(self):
        form = self.schema().load(request.get_json())
        variables = [self.model(**option) for option in form]
        self.service.edit(self.section_name, variables)
        return '', 204

I have tried many solutions that I found online; but they did not fix the issue for me:

1 + pass partial=True to the load function: form = self.schema().load(request.get_json(), partial=True)

2 + remove required=True from the field definition; this made the above error go away but failed many other tests that I have.

I am currently out of ideas, so if anyone has an idea how to fix the issue.