message is actually just a byte array. The prefix string only contains ASCII-7 characters, so it doesn't really matter how you encode it because ASCII-7, ASCII, UTF-8, UTF-16, etc. will all encode it the same. You then take the encoded bytes of that and append the message length (which is just a byte array, so a simple .length will work) and turn that ...
Make sure that you are providing some withdraw_amount in the Value datafield in Remix IDE. By default it has value as 0.
Consider this answer for your reference.
Let me know if the problem still persists.
I've find out the error you are facing.
When you're running this contract, you ...
This is an rpc call that is implemented across clients and I doubt Parity has any plans to deprecate this, as it would break too many application.
There is however a strong desire to stop support for account management and hence most of the rpcs to do with account management have a deprecation notice.
You can view them here: https://github.com/paritytech/...