Contango charges 0 (zero!) fees on the order size, every time a position is opened, modified or closed.
Fees might be turned on at a later stage, and will be collected in the base currency for longs and in the quote currency for shorts, and accrue to the Contango treasury.
Adding automated orders like stop losses and take profits also incurs 0 (zero!) fees. Traders just pay a reward to cover gas costs for keepers. This reward is now set to 2 times the gas cost, but can vary from 1 to 10 times.
The currency this rewards is charged with depends on the margin posted by the trader:
If the trader posts margin in the base, then it’s taken from the margin.
If the trader posts margin in the quote, then it’s taken from the margin by computing it via oracle prices.
A trader adds a take profit on an ETHDAI position where he posted margin in ETH. The take profit reward is taken from the ETH posted as margin.
A trader adds a take profit on an ETHDAI position where he posted margin in DAI. The take profit reward is taken from the DAI posted as margin, after converting it via oracle price from ETH.
When a SL/TP order is triggered and a position closed you receive the quote currency.