Painting plastic parts

[Mike's money pit]

My son has a 2004 Toyota pick up truck. I hope it’s OK to ask my question here. I have enjoyed reading in this part of the forum and know that there are some experts here. I am trying to repaint one of his fender flares. The paint that was on the fender flare had chipped up. I sanded the flare smooth with 220 grit sandpaper. I didn’t get it as smooth as I thought because you could still see some of the chipped looking areas through the primer. However, after spraying on the primer, it wrinkled up in the same areas after just a couple of minutes. I was using rattle can primer called “scratch wizard” that has paint matched for his truck. I used their paint prep and degreaser solution on the part before priming. I am sure I will have to sand this off. The worst of the bubbles are in the same place that it originally chipped up. Thanks for any advice.