EURO function has been removed from Spread's built-in functions as this function doesn't belong to Excel's function list. Further, in v12, with the new feature Language Package, the name EURO will conflict with DOLLAR function in Dutch language.

For backward compatibility, you can use the following code to add the EURO function as a custom function:

fpSpread1.AddCustomFunction(new GrapeCity.Spreadsheet.Win.EuroFunction());