Why does the paint chip every time i spray it?

im painting the headlight bezel (which is plastic) to a 1991 firebird using satin black krylon fusion. the first bezel i sprayed looked perfect but when i sprayed the fusion clear the paint started to chip. as for the second one when i painted it the first time, it had a few paint bubbles so i sanded them down and when i re sprayed it with the fusion satin black it chipped as well and every time i sand it it keeps doing the same thing.