Truncal sip appears unreachable behind the Fortinet 60f using Issabel Pbx

Good evening, I hope you can help me get out of this predicament, I have been trying to register my Issabel Pbx exchange to a trunk of the Dominican Claro telephone company for a few days. The Pbx is behind the Fortinet 60f.

At the moment I have a Huawei router which has the VPN configured to connect to the Sip server of Claro, on the other hand I also have Internet service from the same telephone company on the network through another Huawei router, I have two Fortinet interfaces, each one connected to the Huawei routers, I have also configured the routes to the Internet and to the trunk and their respective policies, I have also configured the VIP ports with their respective policies as well, the The issue is that I have access to the internet from the Pbx and I can also pin both the trunk gateway and the IP address of the SIP server, of course, calls between local extensions work well and also with external extensions connected via the Internet, But when the PBX tries to register, it receives the message that the trunk is unreachable, which is why it does not allow calls to be made outside the network.

Claro-SIP 172.31.21.x   Auto (No) No 5060 UNREACHABLE
Below I post the connection configuration to the trunk with the data provided by the telephone company:

type=peer
qualify=yes
insecure=invite, port
host=172.31.21.x
dtmfmode=rfc2833
disallow=all
canreinvite=no
allow=ulaw

Note before I had the same environment and it worked perfectly behind an Edgmax router, the failure was generated when changing to the Fortinet.

I thank you in advance for your collaboration.