If you are someone who uses Facebook to log into Instagram, it will not work with Tag Post Wizard.
If you use Facebook to log into Tag Post Wizard, you will see this error
You need to sign directly into Instagram for the Tag Post Wizard to work. If you do not know your Instagram specific password, please go here to reset: https://www.instagram.com/accounts/password/change/
You can use 2FA in Instagram to log in. Once you enter your username and password for Instagram, you'll see this screen
Enter the code sent, and you'll be able to start searching.