Bi\HighestBidder is actually a ObjectValue on workspace and this script is inside a text label.
Error appears on line 6
local Bidder = workspace.HighestBidder script.Parent.Text = "Highest Bidder: Nobody" Bidder.Changed:Connect(function() script.Parent.Text = "Highest Bidder: "..Bidder.Value end)
Your value is most likely an ObjectValue, and thus stores a string rather than an object (which is considered UserData). To solve this, you can either store the bidder's in a StringValue in the first place, or just add .Name
at the end of the line:
local Bidder = workspace.HighestBidder script.Parent.Text = "Highest Bidder: Nobody" Bidder.Changed:Connect(function() script.Parent.Text = "Highest Bidder: "..Bidder.Value.Name end)