[Freeswitch-users] Play Credit before disconnecting call

Hi Guys, I have some subscribers connected to my FS. I'm assigning each one of them some credit to place outbound calls and I'm using nibblebill to update balance accordly. I'm rather familiar with LUA, as I'm using a script to make my logic decision on who is calling, which is the remote gateway to use and the tariff to give to nibblebill before bridging the call, and so on. Now, I would like the user to let know the remaining balance at the end of each call playing a TTS message (of course only played when the remote party hang-up) Is this possible? How can I know from which side the call has been disconnected and only play TTS when is the remote party? Thank you so much, I can't find any clue in previous messages. Cheers Max