Why is my RemoteFunction printing nil?

LocalScript:

local player = game.Players.LocalPlayer
local UIS = game:GetService("UserInputService")

local debounce1 = true
local animation = game.ReplicatedStorage.anims.shoot

UIS.InputBegan:Connect(function(key, gameproccessed)
    if key.UserInputType == Enum.UserInputType.MouseButton1 then
        if debounce1 then
            debounce1 = false

            game.ReplicatedStorage.ClickEvent:FireServer(animation)

            local length =          game.ReplicatedStorage.ClickEventReturn:InvokeServer(animation) -- where it fires from

            wait(length + 0.1)

            debounce1 = true
        end
    end
end)

Script:

function send(player, animation)
    print(player, animation) -- prints "nil nil"

    local track = Instance.new("Humanoid"):LoadAnimation(animation) -- errors

    print(track.Length)

    return track.Length
end

game.ReplicatedStorage.ClickEventReturn.OnServerInvoke = send()

This for some reason is printing nil, when i specified the argument in the localscript. And i assume the first argument would be the player. Whats wrong here?

Help pls

Thx