Why I Can't give Perks to Players with Game Pass?

Hello.

Problem

You used LocalPlayer in a ServerScript. ServerScript's run on a physical server instead of a client, so LocalPlayer will always return nil/nothing.

Solution

Remove the player variable on the main scope. There is no need for the variable as the player is automatically obtained using the PlayerAdded parameter.

Fixed Code:

local market = game:GetService("MarketplaceService")

game.Players.PlayerAdded:Connect(function(player)
    if market:UserOwnsGamePassAsync(player.UserId, 9174386) then
        print("Owns the game pass")
    end
end)