Why is my statement split into 'Main balance' and 'Instalment plan' balance?

If you've got an instalment plan, you'll see this as well as your main balance on your monthly statement.

Your main balance is any purchases you’ve made, cash withdrawals, or promotional balances.

Your instalment plan balance includes the one-off fee and any purchases you've moved to that plan.

They’re both included in your existing credit limit and are added together to make your overall account balance.