I tried contacting their support to try to get that fee waived since it seems like an unfair charge. Support claims that the charge 'do not go to us at all, as it was used to process this transaction on the blockchain'
May I know if this is accurate?
They're telling the truth. (
more of "half the truth" or due to the answer not being technical)
If they want to spend that specific UTXO with an alleged "
dust" amount, its amount would just be enough to cover for the size that it will add to their consolidation transaction.
But in cases when the deposit is close to the maximum dust amount that they've set and the average fee rate is relatively small, any excess amount after the fee will go to them.
For example: if that deposit is about 5000 satoshi given the deposit address is a P2SH-SegWit
and it's used as an input when they consolidate multiple deposits that they've received from their customers:
It will add about 91 vBytes (
approx) to the overall size of the transaction, so for example; at 10sat/vB, it will need about 910satoshi to spend it.
In this case, they gain about 4090satoshi from that non-credited deposit.
But if the deposit is about 1000satoshi and the fee that they have to use is 20sat/vB (
when fee is high), it will need about 1820satoshi to spend it.
In this case, they will have to provide an additional 820 satoshi to spend it.
Overall, it's based from the approximate transaction fee and the dust amount their users have deposited.
(
the maximum is a bit high though, probably because they don't want any financial loss)