Are you on the sandbox mode or on the production mode?

I found the root cause of the problem. Your sandbox account is a new one and there are some changes in the phone (digital line) selection option, that force developer to chose either an existing desk phone or the RC app. Before the option was an existing desk phone or the RingCentral soft phone. Because of this, you cannot start using the soft phone to set the emergency address and the RC app for sandbox has an issue to save the emergency address. The problem has been reported and the team is investigating and fixing it.

I don't have a workaround solution right now for you to use the RC app or the RingCentral soft phone.

I'll update you when the problem is fixed as soon as I get the status.

Sure, I will be waiting. Thanks!