2👍
You are right, that is the reason why the signal does not get called since signals are sent at the very end of the view if the model’s verify succeed.
Your solution is indeed wrong, Paypal will definitely send a GET request with the transaction ID to your app url if you choosed to use PDN.
I really suggest you to check your settings (on paypal account) since you are probably using IPN which uses POST requests.
Another possible cause of this is that after you received the GET request from paypal your app sends the POST data to your app instead of to paypal postback endpoint. (https://github.com/johnboxall/django-paypal/blob/master/standard/pdt/models.py#L47)
I would look at the access logs to see if the POST request comes after a GET request (for the same url), if yes I would check the value of the SANDBOX_POSTBACK_ENDPOINT and POSTBACK_ENDPOINT settings.