AS> Where i can found a documentation to configure the direct access to
 AS> connect a old pots modem?
 AS> 
 AS>  g0> Mystic supports direct serial I/O using mgetty.

You would have to use the mgetty documentation to learn how to get it to answer and run Mystic.  mgetty should be able to execute anything with its login configuration and all you should have to do is tell it to run Mystic.

I believe you can have it run ./mystic -ST3 so that the BD MCI code will return the connection type as MODEM.

There may be a few kinks to work out but thats basically it.

... Confucius say: "Its stuffy inside fortune cookie"

--- Mystic BBS v1.12 A47 2021/08/17 (Windows/64)