Error chat not found
If you try to publish a post and receive the error "Unable to publish post" and see the phrase chat not found in the details, something like this:

the reasons may be the following:
- the channel/chat to which Telepost was linked has been deleted, or the bot has simply been removed from the admin list.
- the Telepost bot lacks permission to edit channel information (the bot will also use this permission to check for the channel's existence):

Solution
Please check and fix the following:
- the channel/chat actually exists (not deleted), and the Telepost bot has been added as an administrator.
- the bot has sufficient rights: at a minimum, it needs permissions to edit channel information and manage messages.