How to fix pam_unix error?

Question

linux

Good day.
I have this situation: there is a chat on the site (via socket). Everything worked well. The server returned the result.
Everything was covered yesterday. The answer with the code 502 began to come
. Can you tell me what this is about? I'm not good at administration.
In accordance with the answer received from the user toster, the answer - corrected the question.