We don't currently support auctions for ERC1155 NFTs.
ERC1155 NFTs are semi-fungible items that allow for more than one owner of the same token ID.
Below, you'll notice that there are multiple owners and listings present on the same item page.
OpenSea currently does not support auctions for this kind of NFT.
If you own an ERC 721 NFT (known as 1/1 NFTs), you'll see the option to set up an auction.