Error 10002 - Security header is not valid

After these last updates I started to get an error from PayPal API: "Error 10002 - Security header is not valid". After some reseach, I found the change that is causing the issue:

https://github.com/tangentlabs/django-oscar-paypal/commit/5532ed3c842481e62a33ef4823af1420449b063d#diff-78da9f86d1ad48af1eccc703b5e28c22R22