Since Accounting Start is designed for a single user, you will not have the option to invite a new user via User Management.
To grant access to your accountant, he or she will need to sign up for the Accounting Accountants Edition. This will allow your accountant to establish a link between your accounts and access your account from the Accountants Edition. To do this:
NOTE: While this is required for your accountant to gain access to your Accounting Start account, this is also the recommended process for accountants working with clients using Accounting. Even though Accounting supports multiple users, we recommend that accountants sign up for the Accountants Edition to access their client's data for the best overall experience