received IRS letter stating interest earned for my deceased parents from payer's FID 38-1798424. How do I find the the payer?

[MonikaK1]

Another user in this thread identified that ID as belonging to the IRS. An Internet search will bring up other sources concurring that this is a number IRS uses for reporting interest they paid. If an income tax return is being prepared for them, either a Form 1040 or 1041, the amount can just be entered as interest from the IRS.

This IRS webpage describes other ID matching programs taxpayers can use to find out who is issuing a document.