we also tested it on our main server and get this same error
we have been using this [Release] [ESX] /transfervehicle (Simple script addon to transfer your vehicles) with no errors but @Heady20006 has good work and i liking using his work so i have added it to out server and we just get this error when we are half way into using contract if you like ill record me giving a car and getting this error to show proof i get it from using this
also everything works with no problems the other player gets the car and they can give it back but just get this half way into it so trying to find out why