I'm trying to use a sub account to automatically sort payments made on this account to a certain category (car stuff). So I don't want to move money in or out there, it's just so that all my car related transactions will have this particular account number and it's a way to automatically label it and easily filter out all my car related payments when filing taxes.
For this purpose, it would be ideal if I don't have to transfer money to this sub account, but could simply have it act like a proxy, having the same funds available as my main account. It would also work if I could automatically re-fill this account from my main account, but that would still limit the amount of funds available on this sub account and whatever buffer I keep there would not be available through my main account.
Would be great if you could just use a sub account like with gmail, where you can put a + sign and it just goes to your inbox, but you can sort it out because it's a different "to" than your normal emails (bla+something@gmail.com goes to the same inbox as bla@gmail.com).