The admin sets the fees in the coin adapter settings via the admin interface.
Every coin adapter has its own way of doing this, but ultimately they all report back to the plugin 4 values: https://github.com/dashed-slug/wallets/blob/5.0.12/includes/coin-adapter.php#L555-L613
When you do a call to the get_coins_info JSON-API endpoint, you get back a number of fields for each coin.
The relevant fields for fees are: “move_fee”,”move_fee_proportional”,”withdraw_fee”,”withdraw_fee_proportional”:0
So, for an internal transfer, the fee paid will be move_fee + amount * move_fee proportional.
For withdrawals, the fee to be paid will be withdraw_fee + amount * withdraw_fee_proportional.
This allows for both fixed fees and fees that are proportional to the transacted amount.
with regards