Custom app distribution through Apple Business Manager
All apps on the general App Store are also available on Apple Business Manager, you upload to the App Store or test flight. If that works, you’re done - congratulations selling your app to businesses.
When you set pricing, you can optionally choose educational or volume pricing that is different than the general store.
Then, your customers use Apple Business or Volume Purchase Program to buy your apps.

https://developer.apple.com/support/volume-purchase-and-custom-apps/

Read the portion about private apps if that’s your end goal.


From the App Store Connect Homepage, click My Apps, and select your app from the list.
Under Pricing and Availability, go to the Distribution for Business and Education section.
Select “Available on the App Store, for volume purchasing on Apple Business Manager, and for volume purchasing at a reduced price on Apple School Manager”.


Again, you just upload the apps, then set pricing and discounts when the app is approved for sale but before you make it generally available. The people buying have to sign up for VPP or ABM and then tell you their ID for private label apps. Or ask your prospective clients to do this one thing:

Provide your developer with either the Organization ID from Apple Business Manager or the Managed Apple ID of your administrator.

Your is you in this case and you would set custom pricing and availability for their account.