Users can choose between three Bitcoin on-chain Withdrawal Fee options:
Priority - User pays the highest Withdrawal Fee and Bitaroo pays a high miner fee, aimed to get users' withdrawals confirmed relatively quickly.
Standard - User pays medium Withdrawal Fee and Bitaroo pays a medium miner fee, aimed to get users' withdrawals confirmed in a reasonable time.
Economy - User pays low Withdrawal Fee and Bitaroo pays a low miner fee, could be as low as 1 sat/byte, ideal for HODLers that prefer to pay minimal withdrawal fees and don't mind when exactly their withdrawal will get confirmed.
It is important to note that Bitaroo can only commit to Priority paying higher miner fees than Standard which in turn pays higher fees than Economy. We are unable to commit to an exact miner fee for each withdrawal option due to wallet limitations. All we can control is the fee range, aiming that we don't pay too little or too much. Both of which happened before and will likely happen again.
If you like to speed up an existing unconfirmed withdrawal, you might want to give Child Pays for Parent a go.
Details regarding Bitcoin Withdrawal Fees and all other fees are detailed here.