Debug a Paypal Expresscheckout classes

Hello, I have develop some PHP classes to do an expressCheckout call with API. All is ok but when I do the doExpresscheckout, the paiement is not initiated. I could provide you some restricted FTP access until you accept the project. I have done a example form to do testing. All the job is almost done, I think this is just a small thing to correct. I use the 80.0 VERSION. Thanks,