Why is this EquipTool function not firing like its supposed to?

I'm working on an inventory system with the Roblox backpack disabled. I'm confused here. This block of code isn't working. but things like print() are. I know the event is firing and no errors have been shown.

Server Script:

script.Parent.Items.Equip.OnServerEvent:Connect(function(plr, tool)
    plr.Character:WaitForChild('Humanoid'):EquipTool(tool)
end)

The event is firing and all but the code seems to just seamlessly disappear into the background. Other functions like print() are working just fine in the event (btw this is in a GUI).