why is decal added to part not visible on part when game is run?

There were similar questions asked, and I thought I was doing what they were doing, but when I add a Texture to a decal, its not showing up when the game is played. Decal needs to show up for all players, which is why I'm trying to do it from the server. script is as follows:

local wall = game.Workspace.BackWall
local function onEventFired(player, name, decalId, color)
    print(player.Name, " selected a name ", name.. " "..decalId.." "..color)
    if decalId then
        print("decal selected "..decalId)
        wall.Decal.Texture =  decalId
    end
end
myEvent.OnServerEvent:Connect(onEventFired)

The workspace in the game includes a Decal object, just waiting to be populated:

Workspace
    BackWall
        Script
        Decal

The server output from the prints is:

15:29:37.194  papabean00  selected a name  name1 4748626477 red  -  Server - Script:32
15:29:37.194  decal selected 4748626477  -  Server - Script:34

No errors noted in the output

If I paste that decalID into the Decal.Texture in studio, it shows up fine. but not if the Texture is populated from the script. Any ideas why?