If your practice already uses Nexus, you don't register a new organisation — you join the existing one. There are two ways in.
Your practice's Nexus administrator can invite you from Practice → Team members. You'll receive an email with a sign-up link:
Already have a Nexus account with that email? (For example, you signed up for the free NHS dashboards first.) The page will ask you to sign in rather than create a second account — sign in with your existing password, then open the invitation link again and you'll be joined to the practice. Use Forgot password on the sign-in page if you need to. Your existing password is never changed by an invitation.
If you weren't invited, use the standard registration wizard:
Your practice's own Nexus administrator is notified to approve you. Once they do, you receive an email with a link to set your password and sign in.
Until an admin approves you, signing in shows a *pending approval* screen. If it's taking a while, ask your practice's Nexus administrator to check Practice → Team members — pending members are listed there with an Approve action.
If you work across more than one organisation, you can request to join another from /organisations/join while signed in. Once you belong to more than one, an organisation switcher appears in the header.