Why do you need to authorize my card with the full amount as well as charging my installment amount?

The full outstanding purchase amount is authorized to guarantee future payments.

This enables your merchant or retailer to offer Splitit without application forms and Splitit does not charge interest or fees; even if you pay late (although your credit card provider might so please check).

Please note, your credit card provider may charge interest or fees if you do not clear your balance in full so you should always check this.