fix: certicate request

apps/certificate/serializers.py

@@ -31,7 +31,9 @@ class CertificateRequestSerializer(serializers.ModelSerializer):
         course = validated_data['course']
 
         if Certificate.objects.filter(student=user, course=course, status__in=['pending', 'approved']).exists():
-            raise serializers.ValidationError({"course": "Passwords do not match."})
+            raise serializers.ValidationError({
+                "course": "A certificate request for this course is already pending or approved."
+            })
         return Certificate.objects.create(student=user, course=course)