IPN is not being sent to our server since yesterday, but IPN history claims lots of retries

[Webtail]

(Sorry if this is the wrong board.)

We have following problem with our integration with PayPal (a business account with working integration for several years).

On Sat 2021-03-20, around 10 am CEST, we stopped getting IPNs from PayPal. Every transaction get struck in "Retrying" with response code 500.

We were making changes in our site the night before. After the changes, we got 6 IPNs that worked as they should, and after that that we stopped getting any IPNs.

Today we made several tests. Final one was:

• We made order in our system.
• We paid it via PayPal.
• We found it on IPNs list (in PayPal admin account) with status "Retrying" and status 500.
• We took the IPN message and sent it ourselves to our system (from one of our developer's machine, so also from outside the Azure cloud which hosts our site).
• The IPN handling service sent it back to PayPal and received answer "VERIFIED".

Conclusions:

• We ARE able to receive IPNs and handle them properly.
• We ARE able to simulate PayPal sending us IPN and whole further flow is ok, including PayPal confirming the IPN.
• We DON'T get IPNs from PayPal.

Please help. 

[kfchu]

Yes, it works. 

Thank you.