Preview: this works today, but details can still change.

Globals

source

Type: integer?. Server and client.

ID of the player who sent the network event that is being handled.

Only set while a network event handler runs; nil otherwise. Copy it into a local variable before calling Wait, because another event can change it.

RegisterNetEvent('myshop:buy', function(itemId)
  local player = source
  Wait(100)
  TriggerClientEvent('myshop:bought', player, itemId)
end)