Harmony Hub Extender with existing Z-Stick network

This isn’t entirely a Home Assistant question, but I was curious if someone else had already done it.

I have an existing home-assistant install that is primarily working with my z-wave network via Aeon z-stick. I am trying to add a Harmony Hub Extender to that network. I tried manually by putting the extender in pairing mode and then putting the stick in pairing mode but they did not appear to see each other. I also tried to use Add Node via the webui of home-assistant, but that just errors with “Can’t lock controller for command : add_node”

Has anyone else managed to do this?

TIA.