Hi there - usually when you’re seeing people move through the funnel and get all the way to your checkout page, but not actually check out - one of two things is happening:
(1) The checkout page itself isn’t actually working ← i’d double check to make sure the page itself actually functions as expected. It could be users are hitting an error.
(2) The checkout page is registering as viewed when shoppers haven’t actually hit the page.
Everything looks normal in your flow, so (2) isn’t likely. I’d start with making sure the checkout functions!