Linking existing App to Ionic Pro

Hello! This is my first post on the forum. I have an existing app that I’ve been developing for many months (“ionic-angular”: “3.9.2”). Now I’m trying to link it to my Ionic Pro - Developer account (first time I’m linking an app to my Pro account). Going the root of my app and running “ionic link”, I get the following:

D:\myapp>ionic link
? What would you like to do? Link an existing app on Ionic Pro
| Looking up your apps
Request: GET
Response: 401
{ link: null,
  message: '404 Not Found: The requested URL was not found on the server.  If you entered the URL manually please check your spelling and try again.',

Can anyone advise what the problem might be? I’m running the latest ionic cli version:

D:\myapp>ionic -v

   _             _
  (_) ___  _ __ (_) ___
  | |/ _ \| '_ \| |/ __|
  | | (_) | | | | | (__
  |_|\___/|_| |_|_|\___|  CLI PRO 4.3.1

I’ve no idea if this CLI version works with ionic-angular version 3.9.2.

Turns out that I was already logged in to Ionic via a Pro Starter account I’d set up ages ago that I’d subsequently deleted via the Pro dashboard. There was no ionic logout command that I could see, so I did the following (using an incorrect password):

D:\myapp>ionic login
[WARN] You are already logged in as! Prompting for new credentials.
? Email:
? Password: ********
Logging you out.
> ionic logout
[OK] You are logged out.
[ERROR] Incorrect email or password.

Then I was able to log in via the “ionic link” command.