To sign-up as a deputy, go to https://app.vaultbox.tech/login and click 'Register':
Then enter your details as prompted.
Next, Select the Deputy Only plan.
Next, review the details and terms of service and hit submit:
You will also need to set up Multi-Factor Authentication.
If you have received an email invitation to become a deputy:
You will have received a mail from vaultbox informing you of the request. Click the link that says "Sign Up", and you will see the following screen:
(Similar sign up process as the above)
Enter your details then click 'Next'. You will also need to set up Multi-Factor Authentication.
Note that as a deputy, you do not have your own vaultbox. If you would like to upgrade your account, go to 'Settings', 'Subscription' and 'Change subscription'.