It's important to be on the latest version of Slick to ensure your booking and payment can be processed correctly.
The first step for getting onto the latest version is to close ALL tabs with Slick on, open a new tab and start again. Usually this will load you onto the latest version.
If this still doesn't work for you, scroll down to see how to open Slick in an Incognito window (Chrome Browser)
Step 1: Click on the 3 dots in the top right hand corner:
Step 2: Click 'New Incognito Window':
Step 3: Paste your booking url in the address bar