Really struggling to get this to work, with 2.0.25.
Express & Direct give this...
Error: Payment module configuration error. Please verify the login credentials.
The credentials are replicated from a working osCommerce installation.

Noticed that payflow appears to be used in the module, which differs to the working Dynamic Effects' osCommerce payment module - which appears to use a SOAP interface.
Also, no provision for the API signature or Cert., if that has any bearing.