With the help of this guide, configuring cross-domain tracking is pretty much as easy as counting 1-2-3.
According to Google, Cross-domain tracking makes it possible for Analytics to see sessions on two related sites (such as an eCommerce site and a separate shopping cart site) as a single session. This is sometimes called site linking (google, 2020).
Remember, for the cross-domain tracking to work for both cases, both domains need to be tracked in the same GA property. And you will also need to add both domains to the referral exclusion list of the property.
Note: Make sure to replace the domains in our example above into your own domains.
Hope this helps! 😀👍