First of all please check if the phone configuration is correct and there no DND for that number, also make sure that the phone is not mute and ring mode is on.

"When you add anew phone number into the call forwarding list, make sure that the toggle switch is set to enable" ref: https://support.ringcentral.com/article/Set-up-Ring-Group.html

If issue persist, please check with technical support team here https://support.ringcentral.com/contact-support.html

Hi, yes, the configuration is correct. The phone is not on DND, it is not on mute, and the ring mode is on. The phone does ring if a call comes directly to that extension. It only refuses to ring when part of this Ring Group.