When price level is considered, the value of the multiplier will be less than that suggested by the oversimplified version of multiplier. Why?

As long as the aggregate supply curve slopes upward, any increase in aggregate demand will push up the price level. Higher prices, in turn, will drain off some of the higher real demand by eroding the purchasing power of consumer wealth and by reducing net exports. Thus, inflation reduces the value of the multiplier below what is suggested by the oversimplified formula.