You simply forgot to add the :Clone() function into your code:
game.ReplicatedStorage.GivePlayerItem.OnServerEvent:Connect(function(Player, PlayerName)
local ToolToGive = game.ReplicatedStorage.Card:Clone()
ToolToGive.Parent = game.Players[PlayerName].Backpack
end)
Also backpack is the storage for items that are accessed using the ` key. If you want the cards to go immediately into the hotbar you can insert it into the player’s character.