Answer
Yes, you can use the same bank account to fund multiple investment accounts.
However, please check the correct bank details of the account to which you should transfer your funds. A unique Cash Account held at flatexDEGIRO Bank SE is linked to every unique DEGIRO investment account. The details of the account can be found by clicking on 'Deposit/Withdraw' and then on 'Bank Transfer (SEPA)'. If you are verifying a new bank account, please state the username of the target account in the payment description of your manual transfer and follow the steps described here.