Keep in mind, you must also have a payment gateway through a Merchant Service Provider, integrated and functional, to use Visa Checkout. It is not a stand-alone payment gateway.
Typically, a Merchant Service Provider (also known as an acquiring bank or "acquirer") is a bank or financial institution that processes credit or debit card payments on behalf of a merchant. The acquirer allows merchants to accept credit card payments from the card-issuing banks within an association.
Visa Checkout Flow: When you integrate the Visa Checkout button on your website checkout page and the customer clicks it to finish up a transaction, the customer will at that point be able to either enroll or simply sign in to retrieve their saved card. The card details and address information will be saved in Visa Checkout's data service, which will be retrieved by your gateway. You can then use the retrieved data to help the customer confirm a purchase. The authorization request will then be sent by your gateway for credit card processing. This is why, you must have a merchant service provider and gateway to integrate Visa Checkout.
Additionally, your website must use an online shopping cart and offer products at defined prices which can be added to the site's shopping cart and purchased through the site's standard checkout process before Visa Checkout can be integrated.