Unlockable Content is no longer a feature within the creator flow on Foundation. It was initially designed as a way for creators to attach supplementary materials (like high-res images or full-length videos) to an NFT, off-chain via a link to Google Drive, Dropbox, etc.
Unlockable Content was not on-chain with the NFT; it was hosted on Foundation's servers. We've since decided that while this provides a short-term benefit of more space, it affects the sanctity of the NFT and its long-term provenance. We decided to remove the feature because we want to ensure that the NFTs that are minted and sold on Foundation are represented entirely on-chain and can continue to live on even if Foundation ceases to exist.
If you want to add supplementary material to your NFT going forward, we recommend making this announcement on social media and coordinating with the collector outside of Foundation.
For now, any existing NFTs with Unlockable Content will not be affected and collectors will still have access to those materials. This material will only be visible on Foundation.