The best way to go is to use PJSIP. It looks like you have the configs for both. So I’m not exactly sure what you’re trying. Also, yes, make sure you use one of their new PoPs, they’re trying to put as many people there as they can, and they’re more reliable anyways.
Take a look at this guide for the best way to set up your pjsip trunk, assuming your PBX has a static ip.