Intercom muted with headset

Hi,

I'm an IT tech at a small firm. We are using Zoom phone with Poly CCX 600s. Our CEO used to be able to Intercom his assistant and she would receive a short notification before being able to accept the call. The assistant had a older style headset that would plug into the back of the headset RJ9 port on the Poly phone, but we got a new headset and the Intercom works differently.

The new headset is a Yealink WH64 Wireless Headset. It plugs a micro usb into the phones usb A port and works great except for the intercom function. When the CEO starts an intercom, the assistant's phone will receive no notification and will automatically answer the call. The call is also automatically muted so the assistant is not coming through at all.

Ive tried a Yealink EHS35 micro to rj9 cable and the headset does not detect the desk phone at all, no audio between them even after making sure the phone sends it to the headset.

Any advice or setting I can alter to have at least an auditory notification come through before auto accepting the intercom call.

Thanks in advance!