sip provider: ATT FLEX 3cx version: 15 server: 2012 R2 We just upgraded to 3cx v15 and during test/deployment it worked fine, however in the middle of the following day the dtmf stopped working. So callers would call in, but could not connect to their ext or press anything because the dtmf would not accept the user input. At first I just rebooted the 2012 R2 server and it started to work again but then about within 2-3 hours the dtmf stopped working again. Luckily at that time it was end of business day and I didn't have to the reboot it so I can gather more information. When I had time messing around with the system while it was broken, I learned This would not affect our backup line. so when callers called in using call centric the dtmf worked when our ATT flex line didn't work. Then I figured out that stopping the service "3CX PhoneSystem Media Server" and restarting it would fix the problem. So currently everything is working but i'm concerned this will happen again and trying to get to the bottom of this so i can fix the root issue. Does anyone have an idea how to fix this issue?