Amazon payment button shows the cost in Dollars


Can anyone please help. I have spent many hours trying to sort this issue out.
My website designer has added the Amazon plug in to my website and I have added my seller ID etc but when I test it in Sandbox view after I have added the products into my basket and click the pay by Amazon button the cost is in dollers. I then get a message which reads Important Message
We’re sorry, but there’s a problem with this order. Please contact the merchant directly for assistance in completing this order.
Thank you in advance

To investigate this issue fully please contact Amazon directly.
You can do this by clicking on: [Contact Seller Support|]