How to enable TCP for Asterisk
To allow SIP TCP clients to connect to MOR, it is necessary to enable TCP first.
To enable TCP, edit sip.conf at /etc/asterisk directory. Add these lines in General section:
[general] tcpenable=yes tcpbindaddr=0.0.0.0
Once it is done, reload sip in asterisk CLI, or run
asterisk -rx 'sip reload'
It is important to also choose TCP as Transport in the device settings.