Your ETF portfolio is held outside of Spain at Interactive Brokers (IB). This means that, in addition to the access to inbestMe, you will have a parallel access to IB and, when your first transfer is complete, you will receive a different username (by email) and password (by SMS) than inbestMe.
Although it is not essential that you enter to start investing, it it will be necessary to access IB to: 1) Change the initial temporary password, 2) Record your security questions and 3) Notify your destination bank account in case you request a withdrawal total or partial.
Furthermore, if you are a resident in Spain, as IB is outside of Spain, it will be necessary to present Form 720 to the Treasury, depending on the amount invested.