Make sure to follow the configuration guide for the paytype explanation.
server.lua
Config.Drugs = {
    [1] = { -- Lets add our coke drug
        Label = 'Coke', -- The label/name of the drug
        Item = 'coke_bag', -- The unique spawn name for the item (if you are not sure try giving yourself the item via administrator commands)
        Price = 2000, -- The amount of money it will give you. (you can configure the pay type)
        RequiredAmount = 1, -- The minimum amount of drugs required to sell
        DenyChance = 0 -- The chance that the ped will deny the sale and alert the police. (25 = 25% chance to deny)
    },
    [2] = { -- Lets add one more, our meth drug
        Label = 'Meth', -- The label/name of the drug
        Item = 'meth_bag', -- The unique spawn name for the item (if you are not sure try giving yourself the item via administrator commands)
        Price = 2000, -- The amount of money it will give you. (you can configure the pay type)
        RequiredAmount = 1, -- The minimum amount of drugs required to sell
        DenyChance = 0 -- The chance that the ped will deny the sale and alert the police. (25 = 25% chance to deny)
    },
}