Navigate to admin>payments scroll to find the payment having deferred_payment as its provider and click in the name. You can find more information about the 'pay on delivery' method in the sales flow article.

The first step is to make sure the "deferred_payment" method is enabled in your account under Admin>Payments.

If your account uses some type of deferred payments, the tickets would be created with a "Watiting for payment" status.