There's a gasket ring around the cap and if you find out that the gasket ring is missing, please try to find it back immediately.
This might happen when you are washing the bottle, sometimes the gasket ring gets loosened by the soap or water and hence it falls off.
If the rubber ring falls off again, we suggest putting it back and making a hard twist for once so that it will stick back on it.
If this still doesn't fix the leaking issue, please contact us immediately and we will give you a solution to fix it. 😊