Home Node

If you have a home node to run Sphinx Relay, you will be able to generate a QR code to create a Sphinx account.

With the generated you can register as New User.

Important part is you will not be able to use the same QR code for second time.

Then how can I sign in from multiple accounts?

You will need to backup your key with following;

Sphinx > Profile > Backup your key

With the backed up key, you can login from different devices simultaneously by entering the backed up key to "Enter code..." section.