This is the third time (meaning three different services) something like this has happened to me: A custodial service holds a small amount of my bitcoin. When I want to withdraw all funds to my own Lightning node, the transaction fails with an error message that looks a little like this:
You don't have enough balance to pay the route fees, try a lower amount.
Usually what follows is that I manually lower the amount to send and a dust amount is left in my account which I never withdraw.
What's the problem here? Is it not possible to implement a "send all" function that would deduct the fees from the total amount?