Transaction fees for operators

[kiwiidb]

• A simple per-tx-fee would be adding an extra transaction fee entry in HandleSuccesfulpayment. It is however possible that such a payment might fail because it would put the account below 0. It would be possible to also take the extra fee into account when calculating the fee reserve. However this would further complicate things and it would also mean that users would be unable to send a Lightning payment even though they could pay for the Lightning transaction fee (if they could not pay the max LN fee + internal fee).
• An alternative would be to charge fees for incoming payments, which has the benefit that it would never take the account below 0.
• Another alternative would be automated payouts daily, weekly or monthly based on a users' volume or other factors. Like subscription payments, paid automatically.

[rolznz]

@kiwiidb for the per-tx-fee, I think it's reasonable that if you cannot pay the total amount (amount + any fees) then you should not be able to make the payment. Why do you think this is an issue (apart from additional complexity?)