Charging developer fees in secret contracts



I was wondering if there was a mechanism available for developers to charge fees in payable methods for secret contracts on Discovery, and I don’t understand the secret contract call model well enough to come up with one.

My understanding was that Enigma keeps its own state, and runs the callable contract code in the SputnikVM. The same contract code is deployed on the Ethereum network and can receive calls from web3, as well as modify its own on-chain state.

Is this description correct? And if so, would this mean that fees can only be charged through regular smart contract methods? Or could they also be sent in ENG to the Enigma contract when using an Enigma callable method?