How to find the IMEI for GL520

Hi
I have a GL520 for an off-grid location in USA. The only cell coverage at this location is from Verizon. The built in 1nce SIM won’t connect so I am trying to set up a Verizon SIM which needs the GL520’s IMEI. How can I find this? I’ve seen a comment that the VRM portal ID is the IMEA, but Verizon rejects that as an incorrect format. It expects a 15 digit number with no alpha characters, for example 123 456 789 012 345.
Thanks in advance.
David