Yes. Your account needs to be public for us to get started.
Here’s why: the whole method depends on people being able to see your content. When we engage with someone, they check out your profile and decide whether to follow. If your profile is private there’s nothing for them to see, and almost nobody sends a follow request to an account they’ve only just come across.
If you switch to private partway through your campaign we’ll keep working, but expect your results to drop off noticeably while it stays that way.
If you’re serious about growing your presence, going public gives you the best chance for success.