Your checkout or payment provider shows up as a referral in GA4

Why it happens

The buyer paid on another site and came back. Google's help on unwanted referrals names this case: an ecommerce site that uses a third-party payment processor, where users return to the site after checking out on the processor's domain. When the buyer lands back on your store, the referrer is the payment site. GA4 can then credit that site with the purchase.

Shopify's checkout and Shop Pay domains count as other sites. Shopify's help suggests four kinds of domains for the referral exclusion list (the GA4 name is List unwanted referrals): your store's primary domain, the checkout domain checkout.shopify.com, the Shop Pay domain shop.com, and any external payment provider you use, for example paypal.com. Shopify gives the case of a customer who enters the checkout and then returns to your store to keep shopping. The checkout can then appear as a referral source.

Cross-domain measurement is not set up. Google's cross-domain help says each domain sets its own cookies, so one person on two root domains counts as two users with two sessions. Subdomains can cause self-referrals too, which Google says may mean traffic is attributed incorrectly. With cross-domain measurement, the tag passes the same IDs in a _gl parameter in the address, and GA4 does not count a referral when the page carries it.

Old credit stays with returning buyers. GA4 credits the last source that was not direct. Google's example shows a user whose first session went to another domain: when that user comes back through a bookmark, the second session is credited to the same domain. A buyer once credited to a payment site can keep showing it on later direct visits.

Check it yourself

1. 1In GA4, open Reports > Acquisition > Traffic acquisition. Set the last 7 full days and change the primary dimension to Session source / medium.
2. 2Look for rows with "referral" as the medium and a payment or checkout domain as the source, such as paypal.com, checkout.shopify.com, shop.com or your own domain. Write down each domain exactly as GA4 shows it.
3. 3In GA4 Admin > Data collection and modification > Data streams, open your web stream. Click Configure tag settings > Show all > List unwanted referrals.
4. 4Add one condition for each domain you wrote down. Choose a match type, enter the domain and save. Google allows up to 50 unwanted referrals per data stream.
5. 5List only payment and checkout domains. A domain on this list is no longer shown as a traffic source, so listing a site that really sends you shoppers hides it.
6. 6If your own domain shows up as a referral, open Configure tag settings > Show all > Configure your domains. Check that your store's domains and any checkout domain are there, and that every page loads the same Google tag.
7. 7Compare the days after the change with the days before. The rules work on the pages where your Google tag runs, and only for visits after the change.

For the whole path of a purchase to GA4, see Shopify conversion tracking.

Run the free diagnosis

FAQ

Should I add paypal.com?

If buyers pay with PayPal, yes. Shopify's help gives paypal.com as the example of an external payment provider to exclude.

Does an unwanted referral remove the sale from GA4?

No. Google says the setting tells Analytics that the referrer should not be displayed as a traffic source. The purchase stays.

Why does my own store domain show as a referral?

Usually a missing domain in Configure your domains, or a page without the Google tag. Google's cross-domain help names self-referrals between subdomains as one cause.

Does a purchase sent from a server get the referral too?

It can. A server-sent purchase with a valid session_id joins the session the Google tag collected and takes that session's source. If that session was credited to a payment site, so is the purchase.