How to fix saving sessions?

Question

PHP

Good afternoon.
Site on Bitrix, Debian, nginx+phpfpm, bitrix vm is not used. The domain is now delegated to Yandex, we are delegating the domain to another location. And there was a problem. At the old address, the sessions work fine, when switching to a new address, the sessions are not saved.

When I try to change the same order, I get the following error:

Request processing error. The most likely reasons are: the user has insufficient rights; problems with saving PHP sessions; part of the POST request data is truncated by PHP or the web server.

What to do with it is not clear. We don't have server specialists.
Technical support where we transfer the delegation to this gave the following answer:

Probably, when generating cookies, the user's IP address is still used.
Previously, the user's IP address and the connection's IP address were the same, and the user's IP address was probably taken from the remote_addr variable.
Now the user's IP address and the IP address from which the request comes from do not match due to the fact that requests go through our proxy servers. The IP address can change and this is probably causing problems with sessions.
On your part, you must either change the transmission of the user's IP address to Bitrix (we pass the user's IP address in the X-Real-IP header) or ignore it in cookies.

But from the technical side, what to do where to look is not clear.
If anyone can advise please help. Thank you.

Answer 1

Found a solution: it is necessary for user groups to register a Netmask to bind a session and a Netmask to bind a saved authorization 0.0.0.0