Section 32(2)(b) in The Central Goods and Services Tax Rules, 2017
(b)at the option of the supplier of services, the value in relation to the supply of foreign currency, including money changing, shall be deemed to be-(i)one percent of the gross amount of currency exchanged for an amount up to one lakh rupees, subject to a minimum amount of two hundred and fifty rupees;(ii)one thousand rupees and half of a percent of the gross amount of currency exchanged for an amount exceeding one lakh rupees and up to ten lakh rupees; and(iii)five thousand and five hundred rupees and one tenth of a percent of the gross amount of currency exchanged for an amount exceeding ten lakh rupees, subject to a maximum amount of sixty thousand rupees.