Why does a 400 error appear on a POST request?

Question

Bots

There is a server, the VKontakte bot works from it.
Everything was fine before I turned on redirection from HTTP to HTTPS (disabling now does not help)
After that, the following problem appeared:
If you send a message to the bot with English characters, then everything works fine
But if add Russian characters there, then a 400 Bad Request error appears.

At the same time, a POST request with the same data manually works