Trying to change the body velocity of a player after pressing a certain key?

I'm trying to change the body velocity of the player after they press a certain key. Ideally, I wanted it so after the player pressed a certain key they world be flung upwards and then flung downwards back to the ground. Here is my failed attempt.

adebounce = false
local UIS = game:GetService("UserInputService")
local char = script.Parent
local jumpshiftanim = Instance.new("Animation")
jumpshiftanim.AnimationId = "rbxassetid://example"

local keybind = Enum.KeyCode.LeftShift
local canjump = true

UIS.InputBegan:Connect(function(input,gameprocessed)
	if gameprocessed then return end
	if not canjump then return end

	if input.KeyCode == keybind then
		canjump = false

		local playAnim = char.Humanoid:LoadAnimation(jumpshiftanim)
		playAnim:Play()

		local jump = Instance.new("BodyVelocity")
		local jump2 = Instance.new("BodyVelocity")
		jump.Velocity = Vector3.new(0,50,0)
		jump.Parent = char.HumanoidRootPart 
		adebounce = true
		jump2.Velocity = Vector3.new(0,-700,0)
		jump2.Parent = char.HumanoidRootPart

		for count = 1,8 do
			wait(0,1)
		end
		playAnim:Stop()
		jump:Destroy()
		wait(6)
		jump2:Destroy()
		wait(5)
		canjump = true
	end
end)