Play tone/sound when call is answered

I have the need to play a tone/sound to indicate to the calling party when a call to ring group is answered. Long story but this tone indicates to our call center that the receiving party (the registrant) is on the line because they have no other indication.

To make this even easier, it doesn’t matter to us if every call on the system hears a tone when two lines are connected as this is a special/single purpose instance of FreePBX.

The call flow is currently:
Call comes in to Inbound Route (via URI) → Goes to ring group → Agent in ring group answers.
…and it’s after that last step that we want to play a tone to at least the caller (but it doesn’t matter if both parties hear it)

This tone tells the agent that someone is on the line.

Any help with this would be much appreciated.

Thank you!

You could do this by adding a suitable A option to the dial options, but what is wrong with the use of ring back tone, whilst the caller is waiting, which stops on an answer. Callers will be familiar with that.