If you log into your Hipcamp account and hover over your name in the upper righthand corner, then go to "Your trips," you should be able to click on the upcoming trip. Once you do, there is an option to "cancel" on the righthand side, under photos of the listing that you've booked.
Make sure to confirm the Cancelation Policy that the Host has set by visiting the listing page. If you are within the cancelation window, you will be refunded everything minus the non-refundable Hipcamp service fee, which ranges between 8% and 12% depending on the cost of booking.
This refund can take up to seven business days to post to your account, but usually it's processed much more quickly than that.
If you have any questions about the cancelation policy in place or would like a receipt of your refund, please get in touch with Hipcamp Support.