PayPal Credit acct numbers are found on its statements. If your account is new, you won't have a statement. And you do not use the account number to make payment like you would a plastic card. If you are not given the option to use PayPal Credit on checkout, try a different device. If that does not work, then you must use another payment method linked to your account for the purchase. It is likely PayPal's internal security system is blocking the charge. When PayPal Credit option presents itself at checkout only then you can use it. Keep in mind that, PayPal Credit can decline your purchase after you have completed payment and use another linked payment method so make sure your other funding sources linked to PP account have funds available.