I had a prestashop ecommerce shop installed using paypal and i was getting issues where i could not get a successful payment transaction when using PayPal. I asked the following

"This test you ran shows that the PayPal is working in your situation but I need a way to test if the IP I am using is blocked. I will use this for further test when the problem re-occurs. Please can you show me a website/utility/method of checking to see if an ip address is blocked by PayPal."

The test in the following response can be useful in diagnosing errors to do with PayPal connections.

Hi,

We have recently seen contacts from merchants whose host IPs got blocked by an ISP in-between PayPal and the host, effectively blocking them from reaching PayPal. we do not block these IPs ourselves, this is an issue outside the scope of our company.

You could execute ( or ask your network administrator to do so ) the following commands and send the results to your admin (or host) for further analysis, this will help them to find a definitive fix for this situation.

openssl s_client -connect www.paypal.com:443 ( or the endpoint -url- you use to connect to PayPal)

The IPs used by our systems can be found here :
https://cms.paypal.com/fr/cgi-bin/?cmd=_render-content&content_ID=developer/howto_api_golivechecklist

Also please have a look at this guide: https://ppmts.custhelp.com/app/answers/detail/a_id/733

Regards,
Cosmin.