IRS website for federal tax refund FAQ's - https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions
All or part of your refund, including any amount for the Recovery Rebate Credit, may have been used (offset) to pay off past-due federal tax, state income tax, state unemployment compensation debts, child support, spousal support, or other federal nontax debts, such as student loans. To find out if you may have an offset or if you have questions about an offset, contact the agency to which you owe the debt.
We also may have changed your refund amount because we made changes to your tax return. This may include corrections to any incorrect Recovery Rebate Credit amount. You’ll get a notice explaining the changes. Where’s My Refund? will reflect the reasons for the refund offset when it relates to a change in your tax return.
Tax Topic 203, Refund Offsets for Unpaid Child Support, Certain Federal and State Debts, and Unemployment Compensation Debts has more information about refund offsets.
it happens. you'll have to look at the notice and determine if it's correct. sometimes taxpayers make errors when entering their tax info. on the other hand, if the notice is wrong you'll need to call the number on it. have documents in front of you that support your position. sometimes the foul-up is at the IRS end.