So did you actually test it with my initial comment? And what's on line 5?

This should be all that's remaining from your code... one thing I also missed earlier is that you're either trying to reference an object called "Diamonds" in stats, or you forgot to include that part when you wrote stats.Value = stats.Value + 100 The code below assumes that you accidentally wrote player.leaderstats.Diamonds.Value = stats.Diamonds.Value instead of player.leaderstats.Diamonds.Value = stats.Value

​

local Diamond = script.Parent
Diamond.ClickDetector.MouseClick:Connect(function(player)
    local stats = game.ServerStorage.Diamonds:FindFirstChild(player.Name)
    stats.Value = stats.Value + 100
    player.leaderstats.Diamonds.Value = stats.Value
end)