Although this PayPal version for iThemes Exchange takes more effort and time, the PayPal Standard Secure option is well worth it for the security options for your store.
To use the PayPal Standard Secure payment gateway, your PayPal account must be a Premier account or a Business account.
You can select this option through the iThemes Exchange Setup page or from the Add-ons page.
Once you've enable PayPal Standard Secure, you'll need to create and add the API information from your PayPal account.
First you'll enter your PayPal email address.
Then you'll need to login to PayPal and go to Profile and settings and then My Selling Tools.
On the My Selling Tools page, you go to API Access and click the Update link.
Click on the View API Signature link under the NP/SOAP API Integration section (if this is your first time doing this, the link will say Request API Signature).
The next screen will provide you with your API Username, Password and Signature which you will then copy to the Exchange PayPal Standard Secure settings.
Lastly, from the Profile > My Selling Tools page, you'll go to Website Preferences > Update.
There, you will set the Auto Return option to yes and add the URL provided in the iThemes Exchange PayPal Standard Secure settings as the Return URL.