What does Stripe require from me?

Hi, yesterday I noticed that customers trying to purchase my product were having difficulties with the payment process. Upon closer investigation, I received the following message…

"Action required for PaymentIntent

Use the next_action property of the PaymentIntent to determine the next step required to complete the payment. More info "

I understand that it has something to do with the checkout, but what exactly they expect from me remains a mystery to me.