Pay-Per-View: wrong page redirect after one-time view payment

Hi, I'm using the Pay-Per-View plugin and I'm doing some tests in paypal sandbox mode.
I created a Paypal app from the developers dashboard, the sandbox mode provides me 2 fake accounts: a buyer and a facilitator. I set the facilitator API credentials into the plugin settings.

Now, when I try to do a one-time view payment, I use my fake buyer credentials to login, I confirm the payment and then Paypal redirects me to the home page of my website.
Moreover, the paypal transaction doesn't exists.

How can I resolve this? Where am I doing wrong?
Thank you