Paint cracking?

Stuff out of an aerosol can react IF not the same brand, did it all cure at right heat for right amount of time? Did you wipe it clean with wax and grease remover or maybe even laquer thinner? B sure to give right flash time between coats. Metal needs to be right temp as well as air temp.
Nothing than an not be easily fixed. Just sand it down to bare metal like ^^^ said and go again.