Until you receive the actual notice from the IRS indicating what they are reviewing, you will not know exactly what the issue is. When you receive the notice it should tell you exactly what the IRS is challenging and what documents you need to supply to show that what you claimed is accurate. This inquiry could simply be a random check of whether you are qualified to claim the EIC, or they are checking credits that were claimed, or checking about the stimulus payments, but until the IRS sends you a letter or the status changes on the IRS website, Where's My Refund, all you can do is wait.
