As indicated above, Transaction Code (TC) 290 indicates that “Additional tax as a result of an adjustment to a module which contains a TC 150 transaction.”
A TC 150 return module refers to a filed return, so the additional tax resulted from an adjustment to your return.
However, because the explanations are so vague, you won’t be able to know what the assessment was for until the IRS sends an explanation.
Please see the IRS's Master File Codes for potentially relevant information.
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