Here are the explained steps with info that got it working for me :
First, you need to have a Reddit Vault. To get one just join the r/cryptocurrency Subreddit and the vault button should appear in the Reddit sidebar (mobile only), from there set it up, and you're set to go.
The Collectible Reddit Avatar NFT should appear as a banner on your Reddit Home page, if you haven't seen it yet try scrolling a few posts down, refreshing the page, clearing cache, and what worked for me; connecting to a US server VPN, as it is potentially region blocked in some lesser known countries. I used the free Proton VPN.
When you claim it, and if you want to sell it, then install Metamask wallet extension (do not set it up yet). Then go to your Reddit Vault, click the three dots in the top, and copy your recovery phrase, then in Metamask's setup, select import account using seed phrase and paste that same phrase you copied. You might have already done that to see your Moons token in Metamask. But if you already have a set-up non-Reddit Metamask wallet, then create a new profile in your browser (if it supports that feature, like the Brave Browser) or use another browser, and install a fresh Metamask there.
When you are in, you need to add a new custom network by clicking on the network in the top right and then click the “Add Network” button. Add the Polygon main-net network. To know the details you need to fill in, go to this documentation, the up-to-date details should be at the bottom of the page.
To sell your Avatar NFT on OpenSea, you need some MATIC in your wallet, as there is a tiny fee to list it for sale. Use This Faucet. If it doesn't work then buy, or swap for a dollar or two worth of MATIC like I did.
Now go to OpenSea (if it's blocked, again use the US Server VPN) click the wallet at the top right, and connect your Metamask. Now if you go to your OpenSea profile you should see your Collectible Avatar NFT (if not, look in the “hidden” items tab and un-hide it). Then from there you can list it for sale.
That's it, if I missed anything please tell me, hope you found this helpful.
TLDR: Get a Reddit Vault. Get Avatar NFT from Reddit Home page, which might need US VPN to appear. Install Metamask and import your Reddit vault Recovery Phrase into it in the setup. Add The Polygon Network to Metamask and have a tiny amount of MATIC for selling fees. Go to OpenSea, connect your wallet, and sell the NFT from your profile.
