There is just one step necessary to have APOTS working as a public address with connected microphone/loudspeakers.

Change APOTS port mode to CITO APOTS port (CTIP:491) needs to be re-configured to CITO mode to avoid a need of signaling (accept, close connection):

[12:50:58] ABILIS_CPX:s p ctip:491 device:cito 

COMMAND EXECUTED

[15:25:44] ABILIS_CPX:d p ctip:491       

CTIP:491 - Not Saved (SAVE CONF), Not Refreshed (INIT) ------------------------
Act     DESCR:
Run     card:APOTS-1<1>                 USER:aphone
        OPSTATE:UP        LOG:NO                               TYPE:USER
        signalling:APOTS                                       SS:YES
        DEVICE:CITO       
        NUM:98                          ADDRBOOK-NUM:NUM

	Tip
	The “Not Saved (SAVE CONF)” message is displayed every time the configuration is modified but not saved with the save conf command. The “Not Refreshed (INIT)” message is displayed every time the port configuration is modified but not refreshed with the init ctisys command. These messages will disappear after save conf or init ctisys commands.