Scrape out with a pick/scribe/blade and then brush some clear-coat in the seam. At least it's not grains of sand trapped in there, that looks REALLY shitty, ask me how I know.
Powdercoat requires the same prep as paint, if not more, but because of his high adhesion a lot of shops half-ass the prep process.
Not to mention it being a pretty thick single coat, which will make issues with the prep more obvious than if it was slowly built up thin coats (ie. paint)