1. Log in into merchant interface
2. Obtain f_login
3. Obtain security keys (merchant side)
4. Obtain IV and IV ITSN
5. In each file (auth, auth_response, itsn, refund, settle, void) you have to load the needed keys. Please be careful which keys you use, every time you need to load a key take a look in PHP which key is needed (private or public)
6. Auth.php is the first file you need to run, this is the Authorization call