On mikrotik router create a new schedule
Name: SIP-NAT-AUTOFIX
set interval to 00:01:00
on event:
:if ([/ip firewall connection find src-address=”ipofpabx:5060” and protocol=”udp” and srcnat=no]) do={ :global LastSipTimeout ([:pick [/system clock get date] 0 12] . “_”. [:pick [/system clock get time] 0 9]) }
/ip firewall connection remove [find src-address=”ipofpabx:5060” and protocol=”udp” and srcnat=no]
Save and apply
Ensure you change phone system IP.