Is in-app purchases required in this case?

>It's basically an service where employees...

>Purchasing a subscription/not purchased by individual users/This can be done on the website

>...number of users allowed in the organization

Sounds like a use for Apple's Enterprise program, sans App Store. See the 'Programs' link above.

It comes down to the meaning of

>persons can collaborate

If that represents a digital 'collaboration' then you must use IAP because you are enabling a feature within the app (distributed by Apple and running on Apple equipment using code based on Apple's iOS). For example, if the users are scheduling a meeting using the app then the act of scheduling (but not the meeting) is digital and IAP is required.

Unconvincing is:

>We don't unlock any additional functionality or features. The only difference between the different tiers is the number of users allowed in the organization

That seems to be saying the difference is the number of users allowed to use this functionality/feature - that is the same thing as unlocking 'additional' features (i.e. unlocking the same features on different devices is tantamount to unlocking additional features).

If in-app purchases are required, what do we do about the fact that our subscriptions aren't personal? Since the purchase isn't associated with an individual user of the app, but with the organization the user belongs to, I mean. As far as I know, in-app purchases are associated with a unique Apple ID. In our case, we want the purchase to unlock features (if being able to add more users can be considered a feature) for all of the users that belong to that organization.

Your example of users scheduling meetings is spot on - that's exactly what our service and app does. 🙂

If you want to set it up such that Party 1 pays the fee and then (say 7) Parties 2,3,4,5,6,7,8 get certain features then communicate to Party 1 certain information (e.g. Account number A234VF6524H or an enabling email link) that Party 1 can distribute to other parties. When those parties use that account decrement a counter until 7 people have used that account and allow them to use that account until the subscription ends.

I think CloudKit will work great for this set-up.

You will have to assure Apple that you are only granting that access through IAP.