Paypal errors can be frustrating and hard to debug in PrestaShop. Often the language is very confusing and down right weird. If you happen to get an error message with an error code 10605 that means that you paypal account does not support the currency you are trying to pay with. 

In Paypal you have to add the currencies that you want to take payments in. So there are two solutions, change the payment that your shop takes or to add the currency in your Paypal account that you want to accept. I hope this helped solve your Paypal issue. If you ever need PrestaShop support don't hesitate to reach out to us.