ETH fees in withdraw function

[PaulRBerg]

The design should be the same as in Lockup.

Discussed in #327

^{Originally posted by PaulRBerg November 6, 2024}
We've recently decided to charge ETH fees instead of protocol fees in Lockup. ETH fees make much more sense for Lockup streams per all the reasons provided here.

Now, for Flow streams, the fee is paid in stablecoin. This is not bad, but I wonder if charging in ETH wouldn't be better?

1. More consistency across our fee models
2. Less psychological resistance; the user has to pay a fee in ETH anyway (for the gas), so charging $1 in ETH should feel less pressuring than paying a separate fee in USDC (from the recipient's salary)
3. Charging in ETH means that we are charging the account that withdraws, not the recipient (these accounts might not be the same)

Notes:

• I'm not suggesting to change the implementation now because doing so would cancel the validity of the security audits.
• We will start charging in ~March anyway, so changing the implementation in Flow now would be overkill.

Cc @sablier-labs/everybody for feedback.

Tasks

• Make "batch" function payable #338

[smol-ninja]

Great idea. Does this also mean removing existing implementation of protocol fee?

[PaulRBerg]

Thank you.

TBD if we remove the protocol fees. We should carefully listen to user feedback.