I´m currently making an app for a small business that are located in another part of my country. This is a app just for that one business, and should not be available to others. What is the best way to do this? I need to be able to update, and add functions to the application at a later time. Do I need to put it up on AppStore?
You can distribute an app through the Business and Enterprise programs:
https://developer.apple.com/business/
https://developer.apple.com/programs/enterprise/
You could also use 'TestFlight' but then you would need a new version every 90 days.
.