1. Register at Apple to get an Apple ID. Or check if your company has an Apple ID already on the Apple support pages.
   
   
2. Register for a D-U-N-S number on the Apple D-U-N-S registration page. The D-U-N-S numbers are managed by Dun & Bradstreet and for free.
   
   
3. Register for the Apple Developer Enterprise Program. The membership costs $299 per year.
   It can take up to 4 weeks until Apple processed your information.
   
   
   
   Within a few days after the registration, Apple will probably call you and ask you a few questions to make sure that your intentions for the app are in line with the Apple guidelines. Here are possible questions and some ideas for your answer:
   • Q: What is the name of the company that registers?
     A: The name should be the same that was used to register for the D-U-N-S number.
   • Q: What department does the contact person works in?
     A: Just state the department where you (the contact person for Apple) work.
4. Sign in to the Apple Developer Enterprise Program with your Apple ID to verify that everything works correctly.
   
   

Additional Helpful Information: 

• Apple explains the D-U-N-S number
• Support page from Dun & Bradstreet about Apple Account D-U-N-S numbers