is it possible to do the opposite of this?

I can send messages to discord from Roblox using

function filteringFunction.OnServerInvoke(player, msg)
	local payload = HTTP:JSONEncode({
		content = CHAT:FilterStringForBroadcast(msg,player),
		username = player.Name.." - (#"..player.UserId..")"
	})
	
	HTTP:PostAsync(webhook, payload)
	return "Feedback recieved!"
end

but is there anyway I can do the opposite & get the messages from discord to Roblox? like :GetAsync or something? please help me

Discord has a unique API for doing this. Not sure exactly how it works, but you can find it here.