Paypal Sandbox to do Test payments, how works ?

[ytsejam74]

Hi, i want to testing the payment functionality with paypal in my PS site. I create two sandbox account (one business account for the shop to get money, one premium account for custormer to do payments).  My Issue is that i am unable to complete process payment, inside the premium account the balance is 0 euros, when i try to link a credit card to paypal sandbox account (using a fake creditcard number) paypal stops the process for "number not valid" . I don't understand ?!? The sandbox accounts are FAKE accounts to do FAKE payments, why demand a number of a VALID credit card ?