Why is the aggregate supply curve upward sloping?

At a higher price level, producers are willing to supply more real output.

The Profit Effect: When the price level rises, output prices rise relative to input prices (costs), which raises producers' short-run profit margins. So producers can make more money because it costs way more to buy a product in this case than to produce it before everything has had time to adjust.

The Misperception Effect: producers are fooled by price changes in the short-run. they increase productivity even though the price is not rising relative to other products, all prices are rising.