Telegram error 400: Bad Request: message not found

You referenced a message_id that does not exist in the given chat, or no longer exists, or is not one your bot is allowed to see. Telegram returns this from methods such as pinChatMessage, forwardMessage, copyMessage and setMessageReaction. The closely related message to delete not found and message to edit not found variants carry the method name in the description; the plain form is used by everything else.

Message IDs are scoped to a chat. ID 42 in one chat has nothing to do with ID 42 in another, so combining a stored message_id with the wrong chat_id produces exactly this error. In private chats with a bot the numbering is per conversation; in supergroups and channels it is per chat as well.

This is not a permissions failure. If the bot lacked rights you would get a not enough rights description instead.

{"ok":false,"error_code":400,"description":"Bad Request: message not found"}

Persist (chat_id, message_id) tuples and never a bare message_id. Wrap post-hoc operations (pin, react, forward) in a handler that downgrades this error to a log line, since users deleting messages is normal behaviour and not a fault. Avoid scheduling actions on messages far in the future without re-validating them first.

Like the other not-found variants, this arrives as a plain 400 (BadRequest / TelegramBadRequest); there is no dedicated exception class in any major library, so the description string is what you match. When the failing call is a delete, see the more specific message to delete not found; when the message exists but cannot be touched, you get message can't be edited instead.