Password for unlimited users

Hello I am trying to create an app where unlimited amount of people can use it at the same time but the app I protected by a password.

What plan do I need for this use case? Pro or private?

I don’t need to collect their email or have them create the email or have them as a private user. I simply just need anyone with the password to have access to the app.

Which plan is appropriate. And if it i the private plan, I don’t have to pay for each person that access the app do I?