RingCentral user unable to start a video call with employee from the RingCentral app: Host receives the message "The meeting is over. You cannot join now."

My boss and I both use the RingCentral app to communicate. Normally, to start a video call with me, from within the Messages tab he simply clicks the 'Start Video Call' video icon beside my name. As of yesterday, when he does this, he gets the message "The meeting is over. You cannot join now" and the video call ends itself. I can see him calling me in our messages but cannot answer. This problem does not happen when I am the one calling him.