If your TSA PreCheck is not showing on your Delta boarding pass, there could be several reasons for this:

Missing or Incorrect Known Traveler Number (KTN): Double-check to ensure that you have entered your Known Traveler Number (KTN) correctly into your Delta profile or reservation. Even a minor error in the KTN can prevent TSA PreCheck from being applied to your boarding pass.

Not Eligible for TSA PreCheck: Ensure that you are eligible for TSA PreCheck. Only passengers who have been approved for TSA PreCheck and have a valid membership will receive TSA PreCheck benefits. If you recently applied or renewed your membership, it may take some time for the information to be processed and reflected in your boarding pass.

Booking Method: If you booked your flight through a third-party website or travel agency, the TSA PreCheck information may not have been transmitted to Delta correctly. In such cases, you may need to contact Delta directly to add your KTN to your reservation.

Last-Minute Changes: If you made changes to your reservation close to your departure time, such as switching flights or seats, it's possible that TSA PreCheck did not transfer to the new boarding pass. In this case, you may need to manually update your KTN on the new reservation.

Random Selection: TSA PreCheck is not guaranteed for every flight or passenger, even if you have a valid membership and have added your KTN to your reservation. TSA reserves the right to randomly select passengers for standard screening on any given flight, regardless of TSA PreCheck eligibility.