Login to your SWREG
Get your Shop ID
from the top of the page.
Create a new product
(If you already have a product Just copy its id)Creating A Product
Get the API Key
Your API Password
can be anything you want it to be. Write it down so you have a copy.
Inside of your side go to Manage Billing
(/admin/billing.php) and select SWREG from the drop down. On the next page you will specify the amount and paste the values you copied from SWREG.
You can create optin forms using HTML form creator.
You can add custom fields and copy/paste the code to your 3rd party website.