Hi Jennifer.
As you suggested, I have done the test with free tickets. Effectively with the free tickets the attached file in PDF format is correctly attached to the email that is sent to the client.
I hope the developers will soon find a solution to the problem. We will be waiting for new versions of the addon to solve the problem.
Anyway, if there was a temporary solution to the problem, I would appreciate it if you would let me know.
Thanks again for your help.