Translate paypal pro error messages

I am trying to translate some of the errors in PayPal pros( accepting credit card payments ) on the final stage of the payment when the customer does not enter a valid card number, security code, expiry date etc but cannot find the php file that would have these strings. I looked into pp_pro.php but can't see anything inside there.

Errors I would like to translate is things that appear in a pop up such as:

The transaction cannot be processed. Please enter a valid credit card number and type

Can you please help me locate the right file?

Thanks.

is NOT OpenCart - contained Language Content. Anything else would exist in the corresponding language files.
good Luck!
Ernie
ipc.li/cart/