fixing rules backend error

rowers/views/paymentviews.py

@@ -2,7 +2,7 @@ from django.utils.encoding import force_bytes, force_str
 from rowers.tokens import account_activation_token
 from django.contrib.sites.shortcuts import get_current_site
 from django.utils.http import urlsafe_base64_encode, urlsafe_base64_decode
-
+from django.contrib.auth.backends import ModelBackend
 from rowers.views.statements import *
 from django.core.mail import EmailMessage
 
@@ -817,7 +817,7 @@ def useractivate(request, uidb64, token):  # pragma: no cover
 
         messages.info(
             request, 'Thank you for your email confirmation. You are now signed in to your account.')
-        login(request, user, backend=settings.AUTHENTICATION_BACKENDS[0])
+        login(request, user, backend='django.contrib.auth.backends.ModelBackend')
         url = reverse('workouts_view')
         # if user.rower.rowerplan == 'freecoach':
         #    url+='?next=/rowers/me/teams'