Metaops (https://metaopsgaming.com) demonstrated FIO Crypto Handle capabilities within their in-game menus in a developer demonstration.
It was hinted that the Metaops developers utilized the UnityWebRequest features to communicate with their own API middleware service written in JavaScript that would then communicate with the FIO javascript SDK.
TODO:
Waiting for feedback from Metaops team with information that FIO can use to help standardize the API Interface for Unity to FIO integration for future software
...