Air Player 4 is not for sale yet. The release will be in 2021 Q1.
In the meantime you can use the beta for free.
Make sure to read and follow all instructions on this page!
Air Player V4 for Desktop
- Product Code: APPL__AIR_PLAYER_4_HOME_USE_STANDARD__DESKTOP
- Availability: In Stock
- Ex Tax: 9,999,999.00€