[Graham G3ZVT]

Lots I could comment about there but I'll restrict this post to the one critical item I see it.

SIP ports.

The line 1 settings must match up with a CHAN_SIP extension in RASPBX. Mine is 301, the default port is 5060, there is no reason to change it so put 5060 in Line 1.
No doubt you can append it to the IP address with a colon, but why not just put it in the place provided for it?
The PSTN line must match up to a CHAN_SIP trunk in RASPBX again, the default is 5060 but the ATA cannot use the same port twice on the same network interface so its default is 5061, you must therefore change the trunk's port in RASPBX you do that in the peer settings of the trunk as I posted in #7
port=5061

Call the trunk 1-pstn
the incoming user context, user details, and register string can all be left blank.

Just a word on another type of port
In the SIP tab you may have noticed I have restricted the RTP port range to
16384 - 16484
you should similarly restrict the port range in RASPBX

Settings - Asterisk SIP settings RTP port settings.


Next time port forwarding and security...