We were on the Nieuw Amsterdam in November 2023 and had St. Tropez and Corsica, and they did not have loud speaker music. I believe it was once of the middle cabanas that the Cruising Canucks stated there was a loud speaker in their cabana - Cannes.
I was able to get it applied to a cruise I had already booked by starting with the HAL chat. That person told me that it was possible but that I had to call the Reservation Department. (I took a screenshot of the chat just in case.) I called the reservation department and they had to call the Resolutions Department. I was on hold for about 10 minutes but they were able to do it. I requested an emailed confirmation of my reservation and the teacher OBC showed up on there.
My HAL personal cruise consultant said she couldn't help me so I engaged with the chat on the HAL website and they told me it had to be done through the reservations department, then gave me the number. I would try again and just be patient and persistent.
To have the OBC applied to an upcoming booking, call the Reservation Department at 877-724-5425. I did this today and although I was put on hold for about 10 minutes while the person called the Resolutions Department, I received via email an updated booking confirmation showing the additional OBC added for my November 2023 trip.