Subdomain doesn't work with www?

Question

Domain name market

Good afternoon. There was a problem with the operation of the subdomain, without the www prefix, the subdomain works fine, but only this prefix is ​​present, then nothing works.
I tried to do a 301 redirect, it didn’t help either, on the main domain A, the records are registered for www and for @. In theory it should work.
What could be the problem.
Thank you.

Answer 1

Apache or nginx?
Show config.
And so it's a finger to the sky.

Answer 2

On hosting make rewrite url an option?

Answer 3

The problem may be in the web server configuration. Show her.

Answer 4

What error does it give? server not found or apache/nginx error?