Ref nodes are used to define the orientation and position of the car, as well as the position of the cameras. They consist in a set of 4 nodes that define a coordinate system, along with 2 nodes that define the front of the vehicle.
A single set of refnodes must be present on the vehicle at all times, meaning this should be part of your chassis or body jbeam. A vehicle with no refnodes will fail to spawn.
While refnodes do not need to be precisely centered in the vehicle, all refnodes excluding the corner nodes need to be perfectly aligned with each other in their respective direction, otherwise you might experience camera and/or spawning issues, like the vehicle spawning upside down. You might need to do some adjustements to your jbeam for this to be possible, and in some cases the addition of nodes that serve solely as refNodes might be required.
"refNodes":[ ["ref:", "back:", "left:", "up:", "leftCorner:", "rightCorner:"] ["fr9", "fr10", "fr9l", "fr11", "f7ll", "f7rr"], ],