Require users to accept rental terms when booking through the widget

I have a website that uses the IGMS widget to enable booking directly from the website. I have a rental terms and conditions document that I need guests to accept.

Currently, I can send it to them after they book, but there’s nothing that forces them to accept it then, and I can be left in a situation where a guest has ignored the email requesting them to provide guest details and accept the terms, forcing me to then either cancel their booking and refund their money (while still eating the credit card fee), or let them come anyways and hope nothing goes wrong.

My lawyer would be very happy if they had to check a box saying they’ve read and accept it when they book, so that if anything goes wrong and we wind up in a legal battle, we can say “look, they accepted the terms”.