No the problem is this. I wish to be able to create the user and at the same time put in the full_name in the masquerade field. I don't see this documented clearly. My approach is using SSO so I don't want the user to fill this information by themselves. The SSO user creation process must do this.
I am able to user accounts by POSTing to /api/users/ with payload ( "data" => [
"type" => "users",
"attributes" => [) but not sure how to fill in the full name in that same passage of code.