前日のキャンセルですと、50%のキャンセル料金をいただくことになります。
My understand for this sentence is
"If you cancel the day before, we will get 50% of the cancelling fee" (there's a fixed cancelling fee)
PS. In case my English sentence above is not understandable -> If you cancel the day before, you will have to pay 50% of the canceling fee (for example, a fixed cancelling fee is 100 USD. You cancelled the order so you have to pay 50% of the cancelling fee which is 50 USD )
Please correct me