SE PK Ripper bmx bikes are prone to this same non-sense. I had one crack in the same spot and I had the post inserted correctly, but my crack was caused by the seat post flexing. I just cut the top part off, put a key hole on the seat post tube below the top tube and put a hinged seat clamp on it. Looked like crap but it worked great and helped show the awesome quality of said frame.
What Rad Power ebike is that? The $100 off is a joke, but these cheaper ebikes are kinda disposable to a degree. I have Lectrics so I know.