Issue about donation event tracking with gravity form and paypal addon

Hi,
sorry for bother you, but I have an issue tracking donation through gravity form and paypal addon.
I manage a site of a neurodegenerative diseases research center: https://amicicentrodinoferrari.com/
In that website, we have a page that allows users to donate: https://amicicentrodinoferrari.com/donazione-paypal/?valore=0&idc=1449&t=donazione-libera
In that page, I built a form with gravity form (vers. 1.9.12.1) and paypal standard addon (vers. 2.4), and I want only to track this form submissions, sending to google analytics also donation amount (I’m using your plugin, vers. 2.0.3).
I’m using Google Tag Manager tracking code; I’ve set correctly UA tracking ID, events sending with measurement protocol, with default form.
Submission tracking feed is:
– Event Category: Form
– Event Action: Invia
– Event Label: Donazione
– Event Value: empty
No conditional logic active.

I have tried to fill out the form but nothing happens in google analytics events nor in google real time events.
I have waited for some days, but no events have been tracked.
Thanks a lot