Ecommerce tracking is where most GA4 setups go wrong. Here is the full sequence, in the order a shopper experiences it.
The event sequence
view_item_list, select_item, view_item, add_to_cart, begin_checkout, add_payment_info, purchase — each with an items array.
One tag to rule them all
A single GA4 event tag with a RegEx trigger and the built-in ecommerce option keeps the container small.
Testing the purchase
Use DebugView and compare transaction_id and value against the order confirmation page.