Accepting an external Queueing platform

Has anyone had any success in using a third party queueing platform (we are find Zooms call queues quite limited). We are tying to have our queueing system forward to a Zoom shared line group but it doesn't appear to have the capability to "send busy signal" when all members of the group are in a call.  All the members of the shared group have the "When I'm busy on another call" setting set to "send busy signal" but this doesn't make a difference.