Hello,
This list states that some users managed to get it work: [LIST] Banking Apps on /e/OS
You may try upgrading to /e/OS 4.0.
Recently I faced a similar error message while trying to register the UBS Access app with FP6 /e/OS V4.0. It reported a network error and asked to try later. I switched of WLAN and got it work with mobile data connection (with advanced privacy acticated).