Why was the money issued by the continental congress of little value?

The correct answer is:

The money did not have enough gold and silver to back it up.

During the American Revolution, the colonies and the Continental Congress issued paper money, known as Continental currency, to fund the war effort. This bills of credit were usually flat money, meaning they could not be exchanged for a fixed amount of gold or silver coins upon demand. When too many were issued, inflation resulted in the depreciation of that money.