Add a Ring Group
Go to PBX > Extensions > Ring Groups, click Add.
Configure the ring group.
Ring-Group Number : Use the default number or change the number.
Group Description: Give a name for the ring group to help you identify it.
Ring Strategy: ring all available agents until one answers (as default)
Ring Time: Time in seconds that the phones will ring, max 300 sec.
Extension List: Select the desired extensions to the list.
Destination if no answer: Define what will happen if none of the members in the ring group answer the call in the defined time.
Click Save and Apply.