I am trying to use Paypal Express for a client and have all the API username / password a Signature from Paypal however I am unsure which module to use for Australia paypal express

I have looked and installed the standard paypal and PayPal Pro for osCommerce 2.2MS2+ but neither are functioning correctly for paypal express. The closest I get is the later but I receive the following error when I get to the checkout page:

"Your Website Payments Pro API certificate could not be found. Please check the location in your administration section."

I do not have a API Cert? I have saved the "Signature" as paypal_wpp/cert/cert_key_pem.txt and saved this in the same place to see if this worked but to no avail?

I am at a loss which module to use , if in fact Paypal Express can be used ? I have read the wiki info on paypal but the module suggested is extremely old with no updates that I could see?

What is the advantage of paypal express and has anyone got this working? Is there a cost with PayPal Pro for osCommerce 2.2MS2+ from Paypal end?

Sorry for all the questions but I am a little confused to say the least.

Any assistance would be greatly appreciated.