Post messages in Private Group doesn’t work

Hello,
I have a problem and hope that help are here.

My Bot works well with Public Group. But when I change group settings to Private, bot doesn’t post messajes from the site.
On the site doesn’t appear any after post message. No success, no errors.
In the group, bot is admin with all rights.

On the plugin site I found instruction to make it work but it doesn’t help.

It is possible to post messagest in private group?

Thanks a lot in advance.