For some time now, we've noticed users experiencing issues transferring/conferencing clients with destinations that have an IVR out front.
Significantly often, the call is completed to the destination but during interactivity with that IVR our users can enter whatever number they wish but the tones aren't being sent to the recipient.
I've noticed in the forums here this has been an issue for about 2 years now.
here and here as an example. Both threads trail off into nothing with no explanation or resolution. I've looked to see if this was resolved elsewhere somehow in the community/documentation but I can't find nothing.
As it appears that my org isn't the only one experiencing it, I'm living in hope that someone else found the solution.