Fix missing import

api/serializers.py

@@ -10,6 +10,8 @@ from django.utils.encoding import force_bytes
 from django.core.mail import EmailMessage
 from django.contrib.sites.shortcuts import get_current_site
 
+from api.tokens import account_activation_token
+
 class UserSerializer(serializers.ModelSerializer):
 
     password = serializers.CharField(write_only=True)