The document I received from TSA Precheck gave a combination of digits -
Per TSA:
"For members approved for the TSA PreCheck® Application Program, this number is 9 digits long, can be a combination of numbers and letters and typically begins with TT for those who enrolled through IDEMIA or TE for those who enrolled through Telos both which are official TSA PreCheck® enrollment providers."
So yes my KTN starts with "TT" then a combo of letters and numbers. I can find plenty of examples by searching Google (some people actually post in an image their KTN!) but I did not want to post some random person's KTN to show an example of what the TSA Pre Check KTN looks like. I will contact SAS directly to see what is up. As I said I entered it in late fall without issue (letters/numbers) but no longer able to. Thanks all for the responses.