Google Analytics 4 Developer with implementation guideline for web & application click here
Segment Customer data platform implementation guideline Click here
1. Product Detail Stage
Once a user selects or view an item from the list, send the select_item event with the selected item in an items array parameter.
2. Cart Stage
Measure an item being added to a shopping cart by sending an add_to_cart event with the relevant items in an items array
3. Checkout Stage
Measure the first step in a checkout process by sending a begin_checkout event with one or more items defined with the relevant fields.
4. Purchase Stage
Measure a purchase by sending a purchase event with one or more items defined with the relevant fields.
5. Custom Event
if your want to send a custom event to google analytics make sure your create event parameter both ga4 and datalayer.