If the NS500 (sorry,not familiar with it), has the ability to register an additional SIP trunk, to a provider, then use the link below to configure 3CX as a master Bridge trunk. The Panasonic should be able to register to it. https://www.3cx.com/docs/
Thank you Edi, I tried this solution the 3CX is connected to cloud and the NS500 is after a landed firewall, port 5060 and 35060 in addition to some ports are opened.
I will install the 3CX on a local VM maybe it will work in bridge Trunk
In this case the forwarded port on the firewall will be only 5060, which is the SIP Trunk port form 3CX to Panasonic and 35060 Port must be the also forwarded on my cloud to the 3CX.
Regarding the DID's I will make all the needed after the registration of the Trunk.
Regards