After users buy a product online, they want to feel secure about their purchase. They need confirmation that their purchase went through and that they'll receive it.
A proper thank you page gives them the assurance they need. However, most thank you pages don’t do enough to make users feel in control. Instead, they lack a lot of essential elements and information.
It's not enough to say "Thank you" on the confirmation page. A simple thank you message confirms very little about the user's purchase. This is because it doesn't display any of the information the user entered on the checkout form.