WOPI integration for Co-Authoring

Hello Everyone,

I have implemented WOPI MS OFFICE integration on our systems and everything is working fine for a single user but Co-Authoring is not working for me, I am not able to see the other user on the same document, I have tried everything but I am not able to figure out the Co-Authoring part.

Additionally, I don't have CSPP Plus, do we need CSPP Plus for Co-Authoring on the web to work? 

I have implemented Locks and everything following https://learn.microsoft.com/en-us/microsoft-365/cloud-storage-partner-program/online/ link ,it would be a great help if anyone can help with this 

Thanks