Weekday Cabana Discount with Diamond Pass

One of the benefits with a Diamond Pass is 50% cabana discount on weekdays. This is my first year with Diamond so I’m a little unsure how it works. Two questions — does this need to be reserved in person at Hurricane Harbor (NJ), or can I do it online? I didn’t see the option to utilize the discount in the app, or in the online member portal. When I went directly to the cabana rental page, there is no option there either to make use of the Diamond pass discount. And also, would everyone in my party have to have Diamond passes to use the cabana with me?