After initiating bolus delivery on your t:slim X2 insulin pump or through the t:connect mobile app, you can completely cancel the bolus within ten seconds (i.e., during the "Requesting Bolus" phase). After delivery has started, you can still stop the bolus at any time before it is complete, and the device will notify you of the amount of insulin delivered.
A bolus can be cancelled or stopped on either the insulin pump or mobile app regardless of where the bolus request was initiated. When you stop a bolus after delivery has started, a prompt will ask you to confirm your decision.