The sale must be carried out through the IAP toolkit. Simply put, Apple will charge 30% from each transaction.
According to the introduced paragraph 3.1.1:
Applications can use IAP to sell services related to non-interchangeable Tokens (NFT). Including for creating them (minting), adding them to the list of assets (listing) and transferring them to other users (transferring);
Applications can allow users to view their own NFTs, provided that ownership of the NFT does not lead to unlocking functions within the application;
Applications can allow users to view other users’ NFT collections, provided that the applications do not contain buttons, external links or calls to use purchase mechanisms other than IAP.
According to the introduced paragraph 3.1.5:
▫️applications can help in making transactions or transferring cryptocurrencies. However, this is possible only if the exchange has the appropriate licenses and permits to ensure the exchange of cryptocurrencies in a particular region.