I have an MX800 device that is on Software version: ce 8.1.0 Final b8c0ca3 2016-04-05
It is registered in call manager and for some reason the Meeting button is not available. Is there some way I can add the meeting button back on the Touch 10 panel?
Have you checked that it's correctly added to TMS, and that TMS can access it properly, as the meetings button is something that will be activated once TMS can see it can schedule a conference on it.
If you connect via SSH to the codec, and use the API command: xCommand Booking List, does anything appear? If nothing appears, then either TMS isn't pushing the bookings to the endpoint, or the endpoint isn't receiving them.
In the endpoint logs (eventlog/all.log), you should see something similar to the below:
CuilApp User root(0) about to execute command '/Bookings/List' from .
If there are bookings present on the endpoint, you could try to restart it to see if the meeting icon appears.