How to programatically sell items in OpenSea (Polygon network)?

Question

I'm researching about how can I allow my users mint NFTs on Polygon network from my website (done), and to list those items in Opensea (in Polygon Network).

Opensea SDK

I was researching the Opensea SDK but it seems to work only with Ethereum, and not with Polygon.

Opensea API

I have also been checking the Opensea API but I only find methods to make orders, but not to list for sale.

Seaport

I've been reading about Seaport contract, but the official documentation does not provide information about selling process, and the contract only provides functions to buy (orders).

Anyone has an idea about what flow to follow with OpenSea contracts to list for sale an NFT item created outside OpenZeppelin (ERC-721 tokens)?

Answer 1

Offers and listings (buying & selling) are symmetrical, and are not differentiated in the Seaport contract.

E.g. an offer from Alice to supply an NFT for 1 ether would have the NFT in the offerItems of the order, and 1 ether as a consideration with Alice as the recipient.

If Bob wanted to purchase an NFT, he would instead have 1 ether in the offerItems and 1 NFT as a consideration with Bob as the recipient.

From the documentation:

Orders are fulfilled via one of four methods: Calling one of two "standard" functions, fulfillOrder and fulfillAdvancedOrder, where a second implied order will be constructed with the caller as the offerer, the consideration of the fulfilled order as the offer, and the offer of the fulfilled order as the consideration

See also:

https://docs.opensea.io/reference/create-an-offer

https://docs.opensea.io/reference/create-an-order (really, a listing)

These two APIs accept the same structure (an order) but are subject to different validation criteria.