if its peeling on just bare metal spots..then what your using most likely is not a DTM(direct to metal) product..and needs to have a wash or etch primer put on the bare metal first to allow your black to stick to the bare metal...
fuck it try to blow off the paint with a blower see what happens....sand to bare metal 180 then 220 or 320 then 2k primer it--was it cold when u were sprayn? is ur reducer or thinner match ur room temp