I’m guessing they are subsidizing it. On the how it works page it says “Any message, regardless of its original size, only generates a 32 byte content hash and

I’m guessing they are subsidizing it. On the how it works page it says “Any message, regardless of its original size, only generates a 32 byte content hash and costs about $0.03 to submit to the blockchain.” Also “CrypoProof is free to use because instead of sending each content hash as a separate transaction, CryptoProof combines all the hashes posted during the same hour into a Release. The release simply contains all the content hashes posted that hour.”