Bot cannot leave chat that has been restricted due to supposed violations

[php4fan]

A group where my bot is an admin has recently been restricted by Telegram's Artificial Stupidity for supposedly violating some terms of services - obviously BS but that's irrelevant.

The issue is that when the bot attempts to make a request to leaveChat it gets the error:

Bad Request: CHAT_INVALID

Several issues here:

1. The most egregious, you should always be allowed to leave a chat no matter what as long as the chat exists.
2. The error message should be an English sentence explaining why the request failed, not an internal string ID that only the developers know the meaning of, and that is not documented anywhere in the Bot API documentation.
3. Even that string ID is inconsistent with the one you get with other requests for the same reason: a sendMessage request in the same chat gets the error CHAT_RESTRICTED, while leaveChat gets CHAT_INVALID. CHAT_INVALID is even more meaningless.

[php4fan]

Oh it's even more inconsistent: despite the error message, it turns out the bot actually wans't a member of the chat anymore after the request.
So the request succeeded and returned an error message.

[levlam]

So the request succeeded and returned an error message.

This can be fixed server-side.

Otherwise, you have to assume that any request can return any error, and the error can always be handled by its error code. For example, any error with code 400 means that the request didn't succeed (in your case the service message about the bot leaving the chat failed to be sent) and the request must not be re-sent again.