I agree with the others that it would be good to note that a particular feature in the documentation is part of an add-on and they should contact their CSM if they are interested. You don’t need to get into the details of the licensing, as the CSM would handle that, but just making it known that it is not expected to be in their base product.
Something simple like:
This is an add-on and requires additional licensing or subscriptions to utilize it. For more information, contact your customer success manager.
This would go a long way. What is currently happening is people are reading about this in the documentation, and then asking why they can’t find it in their system. When you have to go find the information on the add-ons and show them it is actually an additional cost, it leaves less-than-positive feelings about it.