The highlighted portion in the below examples is your Mapshare Identifier. Your Garmin Share information must be set to public.
https://share.garmin.com/YOURSHARENAME
https://us0-share.inreach.garmin.com/YOURSHARENAME
To find your IMEI: (1) Hold the power button (located on the top of the device, next to the antenna) until the InReach screen turns on. (2) Press the OK button to display the IMEI. Note: The IMEI can also be found on the InReach under Main Menu > Setup > About This Device