A 406 error is almost always caused by an Apache addon called mod_security, which is a security/firewall feature. For some reason, mod_security is blocking our site's automated check of your page. You'll need to contact your hosting provider to look at the mod_security logs to understand why JFBConnect's automated check is failing and to remove the rule that's blocking it.
With that said, I've just manually checked your website for the same things our automated tool would check for and I don't see any issues. I'd recommend to continue testing and see if you encounter any issues with authentication or other features you want to use in JFBConnect. If you have any problems, just let us know and we'll gladly help investigate however we can.
Thanks,
Alex