How do you login to the softphone using an iPad/iOS in developer sandbox mode?

I still think in iOS, it may not be possible for sandbox mode.. I didn't get any successful solution for this.

I can get this reference: https://forums.developers.ringcentral.com/questions/1289/is-it-possible-to-use-sandbox-account-with-ios-app.html

If someone have solution, he can help here

RC Phone mobile app does not support sandbox mode. The app you installed on your iPad is the same as the RC phone mobile app for your iPhone. Thus, no sandbox mode.