Sometimes retailers may offer a separate rate for booking via mobile. Where this rate is offered, the booking must be completed on the retailer's mobile site rather than their normal desktop site or app.
How do I know that the site is the 'mobile site'?
A 'mobile site' is usually a scaled down version of the retailer's desktop site, so will be a more simple version of their normal site. You would be unable to access the mobile site from a laptop or desktop computer and it will only appear using a browser from your phone or tablet, rather than signing in via the app.