It seems the user extension who logged in the app does not have any "online" device or any device at all. You can double check by calling this API from your code. Or login your account service web to see under the user "Numbers & Phones" section.

Hello @Phong Vu,

We are planning to build a web based calling portal where any user could just input the destination phone number and call to that number (just like in the demo app of Ringcentral call control js app without all those ring central app authorization part).

What should we select as preferred device for this use case?