How Do I Script A Stage Ui Which When You Buy A New Stage You Get A Multiplier?

I would in a module do something like this

local module = {
    ['Stage 1'] = {
        Multiplier = 1,
    },
    ['Stage 2'] = {
        Multiplier = 2,
    },
    ['Stage 3'] = {
        Multiplier = 4,
    },
}

return module

in the script you add coins and gems in do

local module = require(module from above)

local stage = player.Stage.Value -- string value
player.leaderstats.Coins.Value += 1 * module[stage].Multiplier

get next stage

if player.leaderstats.Coins.Value > certainAmount then
    player.leaderstats.Coins.Value = 0
    player.Stage.Value = stage name
end