Hx:298: characters 1-8 : Build failure

Oh, I see…I assumed it was was a part of the Tilemap system.

Apparently, Tilesheet was removed in OpenFL 4 according to this post: Type not found : openfl.display.Tilesheet

It looks like it’s still referenced in the Haxeflixel code if FLX_DRAW_QUADS isn’t set. Take a look at the source code for FlxBaseItem here and you can see where it’s checking for it near the top:

So maybe set it in your project.xml file?