When inviting an existing user to a site using the old user management experience, the following error message shows:
 

We're unable to invite users
X
At least one user has an account that is disabled or suspended. Only an org admin can restore this account. If the account doesn't exist in your organisation, contact support.

Steps to reproduce

1. Find an unmanaged user at site level and toggle off their site access
2. Copy that user's email address and click Invite user
3. Observe the following error message appears:
    

   We’re unable to invite users

   At least one user has an account that is disabled or suspended. Only an org admin can restore this account. If the account doesn’t exist in your organisation, contact support.

Expected behaviour

The error message should say something like "this user already exists but doesn't have site access"

Current behaviour

The error message states "At least one user has an account that is disabled or suspended. Only an org admin can restore this account." This is not correct and in fact all that needs to be done is for the user to be granted site access.