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Babylonians used the Shekel or a single unit of barley as commodity money, including rules of debt in 3000 bc.
Metals were used as proto-money in egypt and babylon by the same period. Europeans are familiar with arm-bands of metal as stores of wealth.
Coinage was invented in the Aegean, India, and China around the same time – the end of the bronze age dark age – in the 700-600s bc. The oldest coin I know of is from the Temple of Artemis at Ephesus.
It is most likely that coinage was NOT developed in the fertile crescent because commodity money was sufficient for the density of land trade.
It is most likely that it developed in the aegean because of the heterogeneity of production and sea trade.
It is most likely that it developed in china because of the political, regulatory and tax structure, and the long distance of trade.
There certainly is universal incentive to create coinage to pay for military service although plunder was enough of an incentive.
I do not know enough about trade patterns in ancient india to speculate on the generation of demand for coinage – or why india was less successful than china in consolidation – I assume it is distance, geography and demographic distances.