Quote Originally Posted by EZorb View Post
What would cause this error using credit cards? "The supplied currency code is either invalid, not supported, not allowed for this merchant or doesn't have an exchange rate. - Your credit card could not be authorized for this reason. Please correct the information and try again or contact us for further assistance."

Did not catch before going Live. Help Please
Most likely not an OPC thing, but can't tell for certain unless you switch off OPC and test again.

Several payment gateways only support transactions initiated in the currency tied to the gateway account. Usually the primary currency of the country the storeowner is in.
Some of Zen Cart's gateway modules allow you to specify which currency your gateway account uses, so that it can pre-convert the amount when customers are shopping in another currency.

You didn't say which gateway you were trying to use when this occurred. Nor which currency you were shopping in, and which currency is your store's default, and which currency your gateway requires you to transact in.