The problem Privacy Preserving Subscriptions solves

Subscriptions form the best business models for internet today. We built staked subscriptions for ethereum different from EIP-1337 as we believe the staked architecture presents a lot of advantages over EIP-1337. The amount staked by the user is lent out to a liquidity pool like Compound / Uniswap. This allows the platform to monetize the stakes without any net cost to the user. This model would especially beneficial to low-cost subscription platform like text(think Wall Street Journal) as well as other relatively low-cost subscription models.
We also combined this model with ZK proofs to anonymize the actual service people subscribe to.

Demo contract is on the mainnet and actually integrated with live compound money markets.

Challenges we ran into

We used the Aztech protocol for zero-knowledge proof functionality,
Decrypted the closed source the compound finance API interfaces and built them into smart contracts.
Integrations with AZTEC were especially challenging but we managed to come up with a depoyable codebase in this time.
Decide in which proof validator we need to use in our project. After a long discussion with Aztech team, we decided to use

Range proof

validators and a custom zkAsset(ERC-1724)SMART CONTRACT .