PayPal USA, Canada v1.3.9 Module Configuration Issue on Prestashop 1.6.1.1

[Drob08]

_{Can Anyone help me please? I have been trying to set-up PayPal USA/Canada module version 1.3.9 on Prestashop but when hit save settings it keeps returning INVALID CREDENTIALS message. I am very confused with this. I have the sand box account created and I retrieve all values for PayPal API setting from  this account. what should I enter for PayPal Business Account textbox. I have tried everything on this but nothing seems to be the valid credentials. can anyone share some light on this issue?.  There is not much documentation out there and the Sand Box PayPal website does not have a detailed and concise guideline.}

 

 

_{Thanks in Advance!!!!!!!!!!!!!}