Problem configuring FreePBX to allow outbound calls - "all circuits are busy"


This is my first post on this board so first hi to everyone.
I have been tasked with rebuilding Asterisk after the previous builds died.
I don’t have experience in this area and am a complete newbie so I apologies if my terminology isn’t exact, and I’m happy for any and all suggestions.

Now onto the problem I have set-up the system to the point where I can make internal calls between devices, but I am unable to make calls externally to a mobile device, landlines or any other destination, and when I do it Asterisk replies with “all circuits are busy”.

I am running version FreePBX, on centos, I have thus far created an extension for my phone, added a trunk and tried to create an outbound route.

I believe the problem is in the area of the outbound route? Which I have given a name of ‘default’, added a dial plan of NXXXXXX and set my trunk sequence to ZAP/g1.

Is there anything else I need to configure? and if so what would I do I need to do to allow outbound calls?

thank you for any assistance, if the details I have offered as still to unclear, please say what would been needed to diagnose the issues with the system.

Kind regards