If you're using contactless whilst travelling with TfL, make sure you're using the same device to tap in and out at the card reader. For example, if you tap in with your Apple Watch, be sure to tap out with your Apple Watch also.

If you accidentally tap in or out with a different device for any part of your journey, this will be classed as two separate journeys and the maximum daily cap won't apply.

You can always find more information on contactless payments here.