Well, there's "Walmart Pay", a QR-code based payment system. It seems pretty clear they're refusing to adopt the normal contactless payments, not that they are incapable.

My headcanon is that Walmart pay 1) avoids or circumnavigates traditional credit-card payment processing fees and 2) is accessible for lower income and unbanked/under banked customers.

My understanding is that it's not a matter of figuring it out, it's a choice to not support it.