When I try to save the player.Speed value (the value representing their walkspeed) it didn't save, and I was using the same thing before but it didn't work, it also says that speed is not a valid member of the player. I created the Speed value in a separate script. Datastore script:

local datastoreserv = game:GetService("DataStoreService")
local myData = datastoreserv:GetDataStore("NewData")
 
game.Players.PlayerAdded:Connect(function(player)
    local leaderstats = Instance.new("Folder")
    leaderstats.Name = 'leaderstats'
    leaderstats.Parent = player
 
    local Cash = Instance.new("IntValue")
    Cash.Parent = leaderstats
    Cash.Name = 'Cash'
    
    local codesRedeemed = Instance.new("BoolValue")
    codesRedeemed.Name = "CodeRedeemed"
    codesRedeemed.Value = false
    codesRedeemed.Parent = player
    
    local points = Instance.new("IntValue")
    points.Name = "Points"
    points.Value = 0
    points.Parent = leaderstats
    local speed = player.Speed
    local key = "Player_"..player.UserId
    local data 
    local success, errormessage = pcall(function()
        d`ata = myData:GetAsync(key)
    end)
 
    if success then
        if data then
            Cash.Value = data.Cash
            points.Value = data.Points
            speed.Value = data.Speed
        end
        
        
    else
        warn("ERROR")
        warn(errormessage)
    end
end)
 
game.Players.PlayerRemoving:Connect(function(player)
    local key = "Player_"..player.UserId
    local data = {
        Cash = player.leaderstats.Cash.Value;
        Points = player.leaderstats.Points.Value;
        Speed = player.Speed.Value;
    }
    local success, errormessage = pcall(function()
        myData:SetAsync(key, data)    
    end)
    if success and data then
        print("Data Saved successfully")
    else
        warn(errormessage)
    end
    local Players = game.Players
end)

script used to create the value:

local players = game:GetService("Players")

players.PlayerAdded:Connect(function(player)
    local speed = Instance.new("IntValue")
    speed.Parent = player
    speed.Name = "Speed"
    speed.Value = 16
    player.CharacterAdded:Connect(function(character)
        character:WaitForChild("Humanoid").WalkSpeed = player.Speed.Value
    end)
end) --This is a script that loads your walkspeed on respawn
Anonymous