Zoom meeting won't allows attendees in.

Sign in to the Zoom web portal as an administrator with the privilege to edit account settings. In the navigation menu, click Account Management then Account Settings. In the Meeting tab, verify that Allow participants to join before host is enabled. If the setting is disabled, click the toggle to enable it.26-Sept-2022

I would say this sounds like they have a different link to the meeting than the one you are using? Might you have set up two meetings for the same time perhaps? Make sure they have the same log in link that you are using. The answer from @willjoe2442 above is only relevant if you want people to join the meeting before you get there but it sounds like if they are trying to join and get the message that you are already in a meeting, then it might be more to do with the links you are all using (Ie you have set up 2 different meetings but think it is only one). Perhaps resend your link out again and make sure you are all using the same one? Just a hunch but let me know if that might be it.