If you haven't already you can create a basic checkout item by following
this article.
1. Click on Checkout and then View Checkout Items to see a list of your checkout items.
2. Click the pencil icon to edit the one you would like to update.
3. Scroll down the page just a little to Payment Type and change this from Fixed to Custom.
4. Click on the Add Payment Option button.
5. Decide how many payments you would like and then click on Add Another Day so you can see the number of payments you would like to collect.
6. Enter the day and billing amount of the first payment.
It is recommended to leave the Days From Purchase 1 days at 0 to ensure the user gets charged the first payment immediately.
7. Enter the billing amounts of the rest of the payments and set a day when they should be charged.
For example if you set the Days from Purchase 2 to 30 days then the user will be billed a second time exactly 30 days after they purchased.
8. Click the Add Option button when you are finished.
9. You may repeat steps 4 - 8 as needed if you want to have multiple payment options.
10. Save the page at the bottom by clicking Update Checkout Item.
11. Click on View Checkout Items inside the admin menu.
12. Find the checkout item which you just updated and click the chain link icon.
13. It will now display a popup with all the payment options you have created here. Click the chain link icon again to copy the link to your browser. You can then paste this link into your landing pages, website, or send it directly to a customer to access the checkout page.