Configure Cross Domain Tracking
If you have multiple domains (mystore.com and mylandingsite.com) you need to configure cross-domain tracking in Google Analytics 4 so it can track users as they move from one domain to the other.
Return to your Websites Data Stream settings.
Select "Configure tag settings"
Select "Configure your domains"
Click "Add condition"
Enter your store's domain and add a new condition for each domain that sends data to this Google Analytics 4 property. You only need to add separate root domains (myfirststore.com & mysecondstore.com), not subdomains (first.mystore.com & second.mystore.com).
If your landing pages are hosted on a separate root domain (like mystore.unbounce.com), be sure to add them here.