Message extension doesn't work for a new added chat

MHong2012 

Since the community has not yet responded to your post, you might want to seek assistance with other resources that are focused on tech support:

• Ask your IT manager to open a support case or call Microsoft using the support line you were given.  Other options for business subscription admins are listed here:

https://docs.microsoft.com/en-us/microsoft-365/business-video/get-help-support?view=o365-worldwide#:~:text=Online%20support%201%20Go%20to%20the%20admin%20center,contact%20method%2C%20and%20then%20select%20Contact%20me.%20

https://support.serviceshub.microsoft.com/supportforbusiness/create

• Additional tech support is available at https://support.microsoft.com/ or https://answers.microsoft.com/, where authorized Microsoft agents are available to trouble an issue until it’s resolved.