Trying to create a click to dial, I can make it work for two internal numbers, but I cannot figure out how to define an external number.
ARI has no concept of internal or external numbers. It dials what you tell it to. You would use the same Dial string you would use if doing a Dial from the dialplan itself. You could also use a Local channel instead to execute dialplan logic for dialing.
found the missing piece - endpoint syntax
can you add it to the documentation?