Who came up with the idea to make coins out of metal (like copper) instead of something like paper or wood?

The exact origin of metal coinage is not known, but it is widely believed to have been first developed in the kingdom of Lydia, which was located in what is now modern-day Turkey, around 600 BC. The Lydians were among the first people to mint coins made of electrum, a naturally occurring mixture of gold and silver. These coins were used as a medium of exchange, and their widespread use facilitated trade and commerce in Lydia and beyond. Over time, the practice of minting metal coins spread to other civilizations and regions, and by the 4th century BC, metal coins were in widespread use throughout the Mediterranean world.