PHP checkout of zero won't work, help?

Hi !

I’m working on a wordpress based website. I have several plans that are administrated through the backend. I can change them to any amount and the paypal / updates. When I set it to zero the program doesn’t know what to do.

Is there a string of php code I can insert that will make it so that the and paypal pay option doesn’t show up when the amount is zero.

Any help is appreciated.