Basic usage of Rest API

Sorry, I am not sure what instance means. Does the instance refer to connection to OpenHAB directly for example via local network instead of through cloud service like myopehab.org?
I am most likely trying to get API response from myopehab.org service where I have cloud connection to my OpenHAB.
My OpenHAB device is running on remote location using GSM internet conection outside my local network so I guess I have to use myopehab.org “interface”.

I have tried that before but probably using it wrong because when I copy/paste my command to my Linux terminal I also get “Unauthorized”:
Screenshot at 2021-08-30 20-16-30

Same command generates correct response in myopehab.org API explorer:

I have foud this post from you. I guess you are describing there how to authorize to get API response via myopenhab url. Is that relevant for me in order to get API response from myopenhab.org? If yes I will research that option more deeply.