You have checked that your Telegram flow is properly published and just stopped firing for some reason?
Probably it is the right time to revoke your Telegram bot's API token and update it in ManyChat.
To change your token, go to @Botfather in Telegram and talk to the bot. Command /revoke.
At this step, choose the bot that you wish to generate a new token for.
As your new token is generated, copy it and go back to your ManyChat account.
Go to ManyChat > Settings > Telegram > Revoke token.
Click 'Refresh Token' and insert your new token into the modal window.
In the end, check that your automation is firing. You are all set!