This is what I got from their support.
Questions: 1. with the pro subscription the app will be available on the app store and google store for anyone to download 2. we can enable that users need to register before having access to the information on the app 2.1 can they register using their own domain email or would it need to be a gmail account? 3. one can write a script to link the registration and 3rd party payment gateway?
Answers: #1 - Correct #2 - You need to create a public app where they can first make the registration. Because your production pp will have an authentication (users in whitelist) they can’t open the that app directly before you have added them. You can take registrations from your website etc. as well. #2.1 - They need to use one of these providers Google, Office365, Dropbox, Box, Smartsheet or Salesforce #3 - Yes it’s possible if the gateway has an API connection… for example if you have Google as a database, you can write the connection with the Google script (GAS) if the platform has rest API.