playerpoint rain on command help?

The PlayerAdded event in this code will never run because it is inside the onChatted function which is never called. You are also missing multiple end's in your code.

local isAdmin = {[""] = true, [""] = true, [""] = true}

function onChatted(message, player)
    if message == "pprainplz" and isAdmin[player.Name] then
        game.Workspace.PPRain.Disabled = false
    end
end

game.Players.PlayerAdded:connect(function(player)
    player.Chatted:connect(function(message) 
        onChatted(message, player)
    end)
end)

To further improve this code you can use a function to check if the player is in the table. So you do not have to set each player to true. This function is also not case sensitive.

I also only call the onChatted function if the player is considered an admin. This allows for less code repetition if you wish to make multiple admin commands.

local isAdmin = {"Bob", "Joe"}

function inAdminTable(Name)
    for _,n in pairs(isAdmin) do
        if n:lower() == Name:lower() then
            return true
        end
    end
end

function onChatted(message, player)
    if message == "pprainplz"  then
        game.Workspace.PPRain.Disabled = false
    end
end

game.Players.PlayerAdded:connect(function(player)
    if inAdminTable(player.Name) then
        player.Chatted:connect(function(message) 
            onChatted(message:lower(), player)
        end)
    end
end)