How to activate a different players gui?

If I wanted to have one person type in the name of the person that they want to invite to their party, how would I make it so a GUI pops up on their screen that asks them if they want to join the party or not?

I thought I've seen this before and took a crack at the code. This is what I've come up with.

squads = game.Workspace.Squads
local player = game.Players.LocalPlayer

script.Parent.MouseButton1Down:connect(function()
local persontext = script.Parent.Parent.Person2.Text --Where they type in the name of the player
    if game.Players:FindFirstChild(persontext) ~= nil then --If it can find the player then it goes through
        a = game.Players:FindFirstChild(persontext)
        a.PlayerGui.SquadInvite.Visible = true
    else
        script.Parent.Text = 'Player not found'
    end
end)