can’t place US order with PayPal

I’ve integrated WCMC on my wordpress site. We are a Canadian company and have set up CAD and USD for our products. We have integrated Paypal for CAD purchases and it works no problem.
When we try to purchase from the US with USD it doesn’t work. It says there is something wrong with the payment. But we are using a USD Credit Card that has been used many times for ePurchases.
I have tried different setting, but can’t get it to work. Please help me make this work or I will have to request a refund and go with Shopify. 🙁
Kristine