“[T]he district court erred by failing to give notice to the parties. We ask, then, whether that error was harmless. Lexon argues that, had it received notice, it would have submitted different evidence of the value of its ‘lost collateral’—less than the full amount of the letters of credit. Lexon argues that the lost collateral, while perhaps not being worth the full value of the letters of credit, ‘had at least some economic value.’ However, Lexon never pleaded nor argued in the district court that its damages could be anything less than the full value of the letters of credit—$9,985,500. If the district court did not have an opportunity to rule on an argument, we will not address it on appeal.” Lexon Ins. Co. v. FDIC, No. 20-30173 (Aug. 2, 2021) (footnote and citation omitted) (emphasis added).