*Download the iframeResizer.contentWindow.min.js file from the developer site or from https://beds24.com/include/iframeresizer/3.5.3/iframeResizer.min.js
*Upload the file to your web server and place it in the same directory as your web page.
*Remove any height parameter from your booking page iframe and add the script after the iframe, if necessary change the src path to the location of your iframeResizer.min.js file.