TypeError: an integer is required (got type str)

https://sentry.lqdn.fr/lqdn/soutien/issues/19/

DoesNotExist: Pledge matching query does not exist.
  File "payment/views.py", line 262, in post
    pledge = Pledge.objects.get(transaction=request.POST['vads_identifier'])
  File "django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "django/db/models/query.py", line 379, in get
    self.model._meta.object_name

TypeError: an integer is required (got type str)
(4 additional frame(s) were not displayed)
...
  File "payment/views.py", line 267, in post
    identifier[6:7])

TypeError: an integer is required (got type str)