Testing a POST method using unittest Client()?

Question

Django

I can't understand why when testing the POST method returns me a 404 error.
There is such a class

class CsvToDatabase(APIView):
    permission_classes = (permissions.AllowAny,)
    serializer_class = VendorsCsvSerializer

    def post(self, request, format=None):
        r_data = request.data
        for data in r_data:
            внутренняя логика
            .....
            serializer = VendorsCsvSerializer(data=data)
            try:
                serializer.is_valid(raise_exception=True)
                serializer.save()
            except ValidationError:
                return Response({"errors": (serializer.errors,)},
                                status=status.HTTP_400_BAD_REQUEST)
        else:
            return Response(request.data, status=status.HTTP_200_OK)

And here is a test

class VendorCsvCreateTest(APITestCase):
    def test_vendor_from_csv_create(self):
        url = reverse('csv_vendor_create')
        response = self.client.post(url, data, format='json')
        self.assertEqual(response.status_code, status.HTTP_200_OK)

urls.py

urlpatterns = [
    path('csv_upload/', FileUploadView.as_view(), name='csv_upload'),
    path('from_csv_create/', CsvToDatabase.as_view(), name='csv_vendor_create'),
    path('create/', VendorsCreateView.as_view(), name='vendor_create'),]

In the CsvToDatabase class, I have two statuses: 200 in case of successful loading and 400 in case of failure. I take the same json (data = my json) that works if sent via Postman and I get 404. Where does this status come from? Everything works from the front. But if I pass an empty list instead of data, then everything is OK - it returns 200. That is, the url is working.

Error log

FAIL: test_vendor_from_csv_create (vendors.tests.VendorCsvCreateTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/y700/projects/solution/apps/vendors/tests.py", line 108, in test_vendor_from_csv_create
    self.assertEqual(response.status_code, status.HTTP_200_OK)
AssertionError: 404 != 200

In theory, if the data was not correct, I would have received 400, but not 404 at all.

ps I tend to think what's the matter in content_type. I have data is a list of dictionaries data = [{}, {}] and in

response = self.client.post(url, data, format='json')

format=json is written.
How to specify the appropriate type?