Attempt to perform arithmetic (add) on Instance and number

Script:

game.ReplicatedStorage.UpgradeEvent.OnServerEvent:Connect(function(plr,upgrade)
	
	local reqs = require(game.ReplicatedStorage.Costs)
	
	if upgrade == "Hammer" then
		
		if plr.leaderstats.Coins.Value >= tonumber(reqs.Hammers[plr.Levels.HammerLvl+1].Price) then
			
			plr.leaderstats.Coins.Value -= tonumber(reqs.Hammers[plr.Levels.HammerLvl+1].Price)
			plr.Levels.HammerLvl += 1
			plr.Multiplier += tonumber(reqs.Hammers[plr.Levels.HammerLvl].AddToMultiplier)
			
		end
		
	end
	
	
end)

ModuleScript:

local module = {}

module.Bags = {
	
	[1] = {
		
		Price = "100",
		AddToMax = "10",
		
	},
	
	[2] = {

		Price = "250",
		AddToMax = "20",

	},
	
	[3] = {

		Price = "500",
		AddToMax = "25",

	},
	
	[4] = {

		Price = "1000",
		AddToMax = "50",

	},
	
	[5] = {

		Price = "5000",
		AddToMax = "100",

	},
	
}

module.Hammers = {

	[1] = {

		Price = "100",
		AddToMultiplier = ".10",

	},

	[2] = {

		Price = "250",
		AddToMultiplier = ".20",

	},

	[3] = {

		Price = "500",
		AddToMultiplier = ".25",

	},

	[4] = {

		Price = "1000",
		AddToMultiplier = ".50",

	},

	[5] = {

		Price = "5000",
		AddToMultiplier = "1.00",

	},

}

return module

What am I doing wrong?
For reference I am making a simulator game and I’m using a module script for reference when upgrading hammers/bags.

Error: ServerScriptService.Upgrade:7: attempt to perform arithmetic (add) on Instance and number - Server - Upgrade:7

Are HammerLvl and Multiplier IntValues/NumberValues? If so, you forgot to put .Value at the end of them, All instances of plr.Levels.HammerLvl and plr.Multiplier should end with .Value

Also why does your module use stringed numbers and then convert them back to numbers when they’re used? It would be better to just make them numbers from the start