Fanvil i21 Interphone Interface

For a few days I’ve installed a fanvil i21 door phone. I managed to configure it correctly, but from inside I can not open the door. The phones used are IP Polycom and Gigaset. If I use a mobile phone number instead of an answering machine, the door opens correctly.
The key for opening is *. The PBX used is Trixbox
Both the PBX and the doorphone interface, dtmf tones on rfc2833 are configured.
Can somebody give me dirt?
Thank you

Asterisk uses “the asterisk” for lots of stuff. There was a thread on here a couple of months ago about the process for sending a star to your phone.