How to make a shop open when the player talks to an NPC?

I want to make my shop GUI visible when the player asks my NPC to view the items on sale. I have no idea how to do this, as DialogChoiceSelected does not work with FE, and my game needs to be FE compatible. How will I achieve this?

Try making a Dialog inside an NPC's Head. There Should be "Choice1" and "Choice2" inside, otherwise you can just make more dialog replies.

Try putting this script inside the Dialog:

--MAKE SURE YOU DON'T COPY THE COMMENTS
local Dialog = script.Parent

Dialog.DialogChoiceSelected:connect(function(Player, Choice)
if not Player then return end
-- Choice1 is the name of the reply dialog in which the player will choose inorder to activate the gui, 
if Choice.Name == "Choice1" and Player.PlayerGui:findFirstChild("NAMEOFYORUGUI")--[[this makes sure that the player doesn't receive the same gui twice.]] == nil then

local Gui = script.NAMEOFYOURGUI:clone() -- change NAMEOFYOURGUI to the name of your gui and make sure to put it under the script.
Gui.Parent = Player.PlayerGui
end
end)

Since DialogChoiceSelected does not work with FE, I used a ClickDetector instead. It worked.