The /collections endpoint provides a list of all the collections supported and vetted by OpenSea. To include all collections relevant to a user (including non-whitelisted ones), set the
Each collection in the returned area has an attribute called
primary_asset_contracts with info about the smart contracts belonging to that collection. For example, ERC-1155 contracts maybe have multiple collections all referencing the same contract, but many ERC-721 contracts may all belong to the same collection (dapp).
You can also use this endpoint to find which dapps an account uses, and how many items they own in each - all in one API call!