We have a disconnect problem encountered when the MultiVOIP is configured for FXO. After hanging up the phone, it could take as much as three minutes, or more, in some cases, for it to disconnect.

By default the FXO disconnect is set to Current Loss. Your PBX probably doesn't support current loss. The reason it's taking a long time to disconnect could be because you are using FXO disconnect on Silence Detection.

I recommend using FXO disconnect on Call Progress Tone. First, go to Configuration, Interface, and enable "Disconnect on Call Progress Tone". Then, go Configuration, Regional, set it to Custom and match the Frequencies and Cadances of the busy tone to the re-oder tone of your PBX.

Then when you disconnect, the VOIP sees the re-order tone and it disconnects right away. You may need to call the maker of your PBX to obtain Re-order Tone information for you PBX.