When I enter my credit/debit card information it says contact the merchant.

Typically, this issue happens due to a fraud protection, the USA having the strongest and hardest to bypass. Many times, you will have contacted your bank and informed them about a purchase, and it will still be blocked, showing on our side but not on your banks end. Other options are to continue contacting your bank to find a solution or to register while selecting bank transfer or paypal as the payment option.