Since September 2019 (PSD2), ING no longer offers the transfer function via FinTS / HBCI interface. For this reason, transfers can no longer be made via Outbank.
Please note the information on the bank's website:
"Important for FinTS / HBCI users: You have not been able to make current account transfers with your current software via the FinTS / HBCI interface since September. This will not change in the future either. However, you can see your financial software via the FinTS / HBCI interface furthermore your account balance and the turnover of your current account. Please make your transactions directly in our internet banking. "