Hi,
From AsyncOS 15.5.1 you cannot use load license anymore. They haven't documented this very well at all, and when talking to Cisco support they recommended a document from 2015 which says you should use loadlicense
After trying to explaine there was a lot of trial and error from Cisco support, but they needed to set the hostname, set the administrator password, configure the network and open up the firewall or proxy, you need to be able to reach https://smartreceiver.cisco.com/licservice/license . When that was done we had to create a token in our smart-license account, login to the ESA GUI and register the ESA för smart licensing.
Hope this helps
Michael