With just the settings above in @17.8.2. Setup within Kartris, you will get errors at checkout and in the logs see references that the crypto provider cannot find the file specified (i.e. the .pfx file), even though you have verified that the path to it is correct. For technical reasons, to access the certificate, you need to make an adjustment to the application pool that the site runs in.

1. go to IIS Manager
2. go to the application pool instance
3. click advanced settings
4. Under Process model, set Load User Profile to true

Once this is done, you should be able to checkout and reach the GP Webpay payment pages.