This operation is only used for Tiered Subscription Plans (i.e., plans that have entitle_type=tiered). This operation is used to determine which videos belonging to playlists in your library should be accessible to each Tiered Subscription Plan.
Once you add a playlist to a Tiered Plan, any child playlists (and videos belonging to those child playlists) will also inherit the subscription requirements from that Tiered Plan.
Note: This operation will only add the specified Playlists to the Tiered Plan, it won’t remove any of the existing Playlists associated to it.
Note: If a video is currently monetized with a purchase, rental, or pass plan, and your property does NOT support multiple monetization, then adding that video to a playlist within a tiered subscription will disable the existing purchase, rental, or pass plan paywall and switch the paywall monetization on the video to the tiered subscription plan.