Unable to associate since your Microsoft Account already has an existing Microsoft 365 subscription. Check http://account.micrsoft.com for more information.
In most cases, this issue occurs when you are trying to use a Microsoft Account that already has an active Microsoft 365 subscription purchased through a Microsoft direct or partner channel other than Mac App Store.
Please log in to your account to check the status of your subscription.
If the problem persists, please contact Microsoft Support.