No. You don't need followers or to be an influencer to use onbrand. Event requests need no social account at all; there's no follower minimum.
What do I need to apply for my event? An account and an event. List the event and send your requests to brands. See How Do I Get Free Products? https://www.onbrand.com/help/how-do-i-get-free-products/
What about creator requests? To send a creator request, connect at least one social account that's still active. There's no minimum follower count. See How Do I Connect My Social Media? https://www.onbrand.com/help/how-do-i-connect-my-social-media/ and What Are the Social Media Requirements? https://www.onbrand.com/help/what-are-the-social-media-requirements/
Can I connect a social account anyway? Yes. It's optional for event requests. See What Social Platforms Are Supported? https://www.onbrand.com/help/what-social-platforms-are-supported/
Who can sign up? Anyone 18 or older. Signup asks for your date of birth.