>>531765182
in rocket league every car is a different one, meaning if you have an endo AND an endo with a bottom trim (pic rel for example has titanium white) they're two different cars
in fortnite they're just 1 but when you edit them you can choose the trim aside from the color, in this other pic i own a normal fairlady from an old rocket pass and 7 trims for it
to answer your question, if you only own that one endo with the bottom painted, you can't use the normal endo with no painted trim until you properly get it