PrestaShop /Paypal connection settings -- 2

looking for an expert to fix payment issue on PrestaShop website and optimize the connections with PayPal Some of our customers getting error message - User Authentification Failed , and can not pay . THIS NEED TO BE FIXED . We have two payment options on the checkout page 1. Payment with credit card via PayPal 2. Payment with Paypal account The default method should be the credit card and clients could choose PayPal as a second method. Default currency is Euro . Default language if French . Site is mostly servicing French clients Payment page terms must be in FRENCH language. You are responsible for testing the checkout on YOUR sandbox Paypal account and making sure it works with IE Explorer, FireFox, Chrome BEFORE you move it to production You must be an expert in PayPal checkout processes and APIs. I need this work done in 2 days. We will take 5 days test payments - to see if you fixed the issue to release full payment.