Do you have a PayPal account set up? If so, you need to make sure you have the secondary pay structure to charge directly to your card instead of having a balance in the PayPal account. Unless you do that, PP won't recognize the funding source. I think PP is the only method Larry accepts. I have used my credit card many times through PP just fine with no balance in the PP account.
USPS money orders cost a little more than a Currency Exchange money order but are even more secure than a certified check. They also never expire and are good for over 100 years. They are also almost impossible to counterfeit so the person that receives it can immediately send your purchase out without waiting to cash it. It has been a winner for me. Billrod