While following the tutorial below for Unreal Engine 4.22 and earlier, you find that there is a node missing when creating the blueprint in Unreal Engine 4.23 or above.
For Unreal Engine 4.23 and above, you must use Evaluate Live Link Frame instead of the deprecated "Get Subject Data". The node "Evaluate Live Link Frame" has a new option called "Role" should be set to an Animation.
You must first first add the subject name arkit (case sensitive). This subject name for facial data is always arkit. Before pressing compile, make sure that the role is still Animation role:
Once complete, you can continue with the tutorial. I.e. Drag out from "Data Result" and create your "get curves" node.