Hello guys,
I was away due to family matters, I'm all yours if more help is needed. Marco, is it possible some plugin is blocking calls with blank user agents? Channel_Digital's top is the first thing to check, if it's not that, if the site is not set in offline mode, if there isn't some htaccess change, if there isn't some Cloudflare setting, some security plugin, then... I have no idea, but we can check if you put my paypal and do a test order in sandbox mode. This will give me the IPN call details so I can replicate it.
Thanks