See What is Sezzle Premium, and how do I sign up?
Upgrading to Premium at Checkout
On eligible purchases, you may be offered to upgrade to Sezzle Premium at checkout. To upgrade, all you need to do is slide the indicator to the right so that it appears as purple. Your total will then be updated to include the subscription cost.
Two orders will be created from this transaction: one for your initial order and one for your subscription. This also means that you will be charged twice. One charge will be for the down payment of your order, and the other will be the cost of your subscription, which will be billed monthly from that point.