Subcontractor asking to be paid to perform (many years) late final inspection

I recently sold my home (November 2023). In due diligence, the buyer found an open permit from 2015. It was a sheet metal permit from a kitchen hood install. The sheet metal subcontractor pulled the permit but never called for the final inspection (nor did the GC). The town would not do the inspection without the sub present. I finally got the sub to come out and the permit was closed. Now, I just received an invoice for $400 from the sub. Is this normal? It seems like this cost would have been included in the original project and the sub not closing it out in 2015 was his oversight. As a side note, the GC unfortunately passed away a few years ago, so the sub is my only point of contact here.