Hello, What does IRS code 599 means on a tax transcript?

[Carl]

Apparently, you have or had an issue with a past year's tax return. Could be you didn't file a tax return for a tax year in which the IRS is aware you had income and should have filed, or you are/were delinquent on a prior year's tax liability.

Basically, the compliance technician who received your return in the Refund Hold Unit recorded your return as received and closed the Taxpayer Delinquency Inquiry. (TC 140 or 474 on your transcript).

Your Taxpayer Advocate is now your only point of contact until the issue is resolved. Start at https://www.irs.gov/taxpayer-advocate to find the nearest advocacy office in your location.