OpenSea Verification

[zcor]

Hi, interested in your repository but have been having some issues getting this to verify on OpenSea.

I'd struggled with this pre Vyper 3.0 and was going to take another look at it now, but was pleased to see you'd done the dirty work of creating it already! Deploying to Ropsten testnet, minting an NFT, and trying to validate it using the OpenSea API yields:

https://testnets-api.opensea.io/asset/0x25928784C0f3235A8A711af00E3F5F61CdA7df48/1/validate/

GET /asset/0x25928784C0f3235A8A711af00E3F5F61CdA7df48/1/validate/
HTTP 404 Not Found
Allow: OPTIONS, GET
Content-Type: application/json
Vary: Accept

{
    "success": false
}

Thought to drop this here in case you had any ideas. Otherwise, great work!