Paypal issue

Hi, sorry for my question, before I write this message I read a lot in the support forum to avoid to disturb you.
Anyway I have the following error in my test environment: Fatal error: Class ‘FatalException’ not found in C:xampphtdocstestwp-contentthemesfunding_pressfundinglibPayPalCallerServices.php on line 80
I also find a great problem in paypal registration, I know that you lost a lot of your time to explain users how to do, but can you describe just with few words how register  in paypal site (I think this site changed from your last explanation).
Shortly, in payapal website you can obviously do a lot of things, but what are the correct steps to obtain this value?
Regards
   Giuseppe