This is my understanding:
Step 1. Do open booking(s). Step 2. Itineraries for ~2023-2024 are released. Step 3. Within 90 days of Step 2, you select any of those itineraries, you get the OBC.
Step 4. You pay the additional deposit due.
Step 5. You pay the balance due.
Step 6. While on board you have $500 OBC to treat yourself to a massage, a private dance lesson, a connoisseur list wine, something from the shops, a shore excursion, etc.