Contract not getting listen on opensea mainnet, however shows NFTs in metamask & works on testnet

Hello everyone!

Just as the title says, on opensea testnets mumbai and ropsten, it 'imports' the smart contract to create the collection, however on the polygon mainnet, the same contracts are working perfectly.
The NFTs even show in my wallet on the mainnet, the contract is verified on etherscan & I can mint.
Please check

Is there anything special I have to do for the mainnet opensea to accept my smart contract?

Thank you very much!!

I created a new smart contract and added

import "@openzeppelin/contracts-upgradeable/token/ERC721/IERC721Upgradeable.sol";

Now it seems to work, still, I fail to understand why on the testnet opensea, it worked without it...
Sometimes development makes no sense.