Painted a Rear Spoiler, the finish keeps cracking?

[BingM3]

Any ideas what it is causing this, I placed a primer, then paint. We got the spoiler pre-primed. Made of fiberglass.

The paint looks fine but keeps cracking the finish after it dries. Could there be a chemical reaction?

Fixes to this? Any better pre-preparations needed?

Thanks.

[M-technik-3]

Yes you needed to add a flex agent to it when paint it. Bentley has the instructions for paint the differant types of spoilers.