darn about not having an "unbind option" ...yes I did set the transmitter to S-FHSS mode (and all the other modes and back again as I wasn't having luck w/ S-FHSS initially).
I just can't get this one receiver to bind w/ my 4PX, -yet it did bind w/ another less expensive lower model Futaba controller w/ no issue. (so like in my previous post, I just had to do some swapping of receivers between vehicles until I found one that would re-bind to my 4PX).