You may be paying off more than one purchase at a time, and each purchase has 10 weekly payments, or 'payment plan'.
When you are approved for LatitudePay, you are provided with a spending limit. You can have twelve payment plans, so long as the total of all the plans is within your spending limit.
If the purchase you want to make is over your available limit, you'll need to pay a larger instalment upfront, so you don't exceed your set limit.