Google Ads -> Payment Processor -> Success page

Hi there!

I’m having trouble with purchase attribution in GA4.

When a user clicks on a Google Ads link, they land on my site, get redirected to a payment processor to complete their payment, and then are redirected back to my site after the payment is successful.

However, all purchases are showing up as ‘referral traffic,’ and after excluding the PayPal domain, they’re being reported as ‘Direct’ traffic. This makes it impossible for me to track which campaign or ad is driving conversions, as everything is now categorized under direct traffic.

Do you know how I can fix this issue?