Ususally it's enough to just add the tracking code to your salespage as found in the Digistore backoffice under: Settings - Promocode for Salespage

The code is e.g.:

<script src="https://www.digistore24-scripts.com/service/digistore.js"></script><script type="text/javascript">
digistorePromocode( { "product_id": 12345, "adjust_domain": true } );
</script>

12345 is the id of your product.

The js code modifies all regular A-HREF-Links and append the affiliate to the url.

Example:

Salespage url is: https://www.some-domain.com/salespage/

Checkout button on the sales page is: 

<a href='https://www.checkout-ds24.com/product/12345'>Buy now</a>

The affiliate advertises: https://www.some-domain.com/salespage/?aff=some_affiliate_name

When a buyer follows the affiliate's link, then the js code above changes the checkout button url to: https://www.checkout-ds24.com/product/12345?aff=some_affiliate_name

That's the regular workflow.

However, if you use a custom js button like:

<a onclick="windows.open('https://www.checkout-ds24.com/product/12345')">Buy now</a>

Then our js cannot identify this button and cannot append the affiliate.

The solution is to use our js function: digistoreAppendAffiliateToUrl( string url ) : string

This function appends the affiliate to an url.

In this case use a button like:

<a onclick="windows.open( digistoreAppendAffiliateToUrl( 'https://www.checkout-ds24.com/product/12345') )">Buy now</a>