Pokémon GO Promo Codes October 2020
Niantic will send promo codes to players who haven't logged into Pokémon GO for a while. It used to be that these codes worked for all players, but it seems Niantic has set the codes to be unique for the player they're sent to. They also expire a few days after they've been distributed.
Sometimes, Niantic releases promo codes for promotional materials, though the last time this happened was in 2017.
It wouldn't hurt to try asking friends who have played before to try their codes out, though codes that float around have been reported to work intermittently at best. Some old codes still check out past their expiry date, so give those a try if you want some freebies.
Overall, code hunting is an inefficient way to get free items. The items you would get from a promo code aren't anything special, and you could get most of them for free from the item shop anyway.