During the early 14th century reign of Muhammad bin Tughlaq, expensive invasions across India and his order to attack China by sending a portion of his army over the Himalayas, emptied the precious metal in Sultanate's treasury. He ordered minting of coins from base metals with face value of precious metals. This economic experiment failed because Hindus in his Sultanate minted counterfeit coins from base metal in their homes, which they then used for paying jizya. In the late 14th century, mentions the memoir of Tughlaq dynasty's Sultan Firoz Shah Tughlaq, his predecessor taxed all Hindus but had exempted all Hindu Brahmins from jizya; Firoz Shah extended it over all Hindus. He also announced that any Hindus who converted to Islam would become exempt from taxes and jizya as well as receive gifts from him. On those who chose to remain Hindus, he raised jizya tax rate.