ran into the issue trying to locate UserRefID and found a solution. Apparently, when you follow their "OAuth2/Authorization Guide", you can get the needed data if you run a GET call:

curl --location --request GET 'https://api.honeywell.com/v2/locations?apikey=CONSUMERKEY' --header 'Authorization: Bearer YOURTOKEN'

The JSON that comes out has the UserID. So, it is indeed the UserRefID (2352951) :

"users": [ { "userID": 2352951, "username": "[email protected]", "firstname": "G", "lastname": "D", "created": 16335504, "deleted": -6213596800, "activated": true, "connectedHomeAccountExists": true, "locationRoleMapping": [ { "locationID": 37316221, "role": "Adult", "locationName": "Home", "status": 1 } ], "isOptOut": "False", "isCurrentUser": true }, {

I hope someone finds this useful.