Error: The user has blocked the bot

If, when trying to reply to a message in a dialog, you see this error, it means that the bot on whose behalf you are replying has been blocked by this user.

A bot can be blocked when deleting a chat in the mobile version of Telegram, if the user has not unchecked the corresponding checkbox, or directly, by opening the account information.

You will not be able to write anything to the user until they unblock your bot by clicking the "Restart" button in the dialog window with the bot in Telegram.
In this situation, you can only manually write to the client from a personal or another Telegram account asking them to unblock the bot.