Before the Tang invention, there were many other ways to buy things. Some people had to exchange their personal goods like crops, beads from shells, stones, knives, silk or gold and other precious metals. Coins benefitted trade by providing reliable for their value. Checks were an improvement on carrying around heavy loads of coins, but with a lot of worth.
Paper money had two main advantages over money made out of silver, gold, copper or iron. It was easier to carry around and the copper and iron