When logging on to Isabel 6, you receive this specific error message: To date, no bank accounts have been added to your Isabel 6 subscription. Please contact your bank(s) to add your accounts so you can start working in Isabel 6. Isabel customer Care
If you are a new user, the bank has not linked the bank accounts to Isabel.
Ask the bank to add your accounts. The correct bank details can be found here.
If you are not a new user:
Log out from Isabel 6 and login with the correct Isabel SmartCard.
If this does not solve the issue, you will need to reboot your device.