This tiny ERC-721 contract shows up in MetaMask but not in OpenSea or checkmynft.com. How can I fix it?

Hello,

I'm BM. A very nice and polite guy.

I am working on a tiny ERC-721 contract, have a look here:

https://ipfs.io/ipfs/bafkreihho6jqvpqpmehsffsllbjo2d2nr75b3la6xnpshm5wzkhxcxeury

The minted NFT will actually show up in MetaMask, image and all so that part works.

However it won't show up in checkmynft.com or opensea.com/assets...

Does anyone know what I need to add to the template in order to make it show up in checkmynft.com and opensea.com/assets section as well? I'm looking for exact code, not pseudocode. Kindly reply with working code if you are able to improve the code so that it meets all three requirements (NFT shows up in MetaMask, checkmynft.com and Opensea.com/assets).