This article outlines how fees are charged when using the WebAuth.com wallet or Proton Bridge to deposit or withdraw cryptocurrencies.
There is no service fee charged by Proton for depositing cryptocurrencies.
When withdrawing crypto, the transaction will incur a fee charged by the blockchain to post the transaction. When reviewing the withdrawal order, you will see the amount you've requested, the amount that's being deducted from the fees and the total amount — all quoted in the cryptocurrency you are withdrawing.
The transaction fee is dynamic, refreshed every 2 minutes and will be calculated using the average speed at the time of the transaction.