This error can happen when the default browser on iOs 14.X is not set to Safari. The bank has been notified of the issue. In the meantime, check a workaround below.
What to do next?
- On your iPhone, go to Settings
- Find "Safari"
- Click on "Default Browser App" and temporarily select "Safari" as the default browser
- Try to authenticate using your Santander app again.
You're free to change the default browser back to your preferred one after your authentication is successful.
If you need more information
Check out Apple's official support page on default browser apps.