I had the same problem and I feel your pain! My issue was because the QB administrator email cannot be the same as the one used to invite an employee via Workforce. 

Try the following:

- Open QB

- Goto Employees>Manage Payroll Cloud Services

- Click "Invite employees" and login using your normal account email and password

- In the window showing all the names, check the check box next to the name of the person (on the left) (in my case, it was me, the administrator) IT's VERY IMPORTANT TO CHECK THE BOX ON THE LEFT FIRST!!!

- Click in the window where the email address is, delete it and write in a different email address (I used my personal email)

- Click "Send Invite"

You should get a new invitation to the personal email address. If you don't click that left checkbox first, it won't change your email and will keep sending invitations to the administrator's email address. This has been driving me nuts for months. I'm so glad I finally worked it out. I hope it works for you.