B2B applications should go through the Apples review just like regular applications do, but they will appear in some private store to which you can provide your client access. I understand that in addition to this, the usual rules apply.
This means that you can offer in the App Purchase and block most of the application if the user does not buy a subscription.
I know not if a subscription can be purchased through a volume purchase program.
As a rule, before you enter the "uncharted waters", only having developed your idea, you should just contact Apple about what you like to do. Ultimately, it is their decision that they will approve, so I will not rely on the opinion of someone on the Internet before putting too much effort into it.
You should also be aware that the volume purchase program is only available in the United States.
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