If you get the IRS letter 9021, it means there was an error or mistake that is being corrected. The error may occur if there were data entry mistakes.
If you do not agree, you can submit a request for appeal/protest to the office/individual that sent you the letter. The letter explains how to file a protest. You should file your protest within 30 days from the date of this letter in order to appeal the proposed adjustments with the Independent Office of Appeals.
Also, see Requesting an Appeal You can also call toll-free at 1-800-829-1040, or contact a local IRS office at the Local IRS Office.
Im sorry I didnt clarify that I only got this notification on the Where's my Refund App. I have NOT gotten a letter from the IRS as of yet. I only checked the app bc it's been a month since I filed.
I would suggest contacting the IRS directly by following the instructions here. As they will be able to advise what is going on.