Please firstly ensure to provide feedback to your prior post's => here <=.
Polycom utilizes the RFC MWI method via a SIP NOTIFY so I would check this with Avaya on their end as they would have done the interoperability testing.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services
Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels. Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's