Reddit mentions of SEM 39133 Flexible Primer Surfacer - 13 oz.

Do you have a picture of the damage? Depending how deep it is you’re gonna want to start with 80 or 150 grit. Sand it down as much as you can to level out that scratch. It’s best to use an actual palm sander when doing this otherwise you’re going to be sanding for a while. You must keep the sander moving in an area larger than the scratch....think shaving a layer all around so it’s even and will make your feathering easier. Don’t use traditional bondo, they make plastic filler (https://www.autobodytoolmart.com/evercoat-poly-flex-flexible-polyester-glazing-putty-411-p-15571.aspx?gclid=EAIaIQobChMImYjOtbKS3gIVS0wNCh0_6gLVEAQYASABEgJsm_D_BwE) which has flex in it made for plastic body parts. I use that at work but it’s expensive...you can find a cheaper one. The traditional “bondo” is meant for metal panels and it will crack on a plastic bumper. I put that on before I feather out because you’re gonna want sand that down with 150 also. After you got it nice and level go to 240 and then 320 grit sand paper. Then you may prime it. I usually go 3-4 coats of primer. Sand that down with 600. Ideally you don’t want to just paint right over the primer. I use sealer that is meant for plastic parts but if it’s a DIY at home you can probably get away with not doing that if you wanna save some bucks by using this https://www.amazon.com/SEM-39133-Flexible-Primer-Surfacer/dp/B000HAXLZO So then yes base coat then clear coat. Take your time if you have any questions just ask.