Apple is offering another round of bonuses when you add funds to Apple ID. The offer lasts until May 10 (via MacRumors). 
Apple ID Funds
A bonus for Apple ID Funds of 10% means you get a certain amount of money depending on how much you add. Here are the tiers:
- US$10: US$1.00 bonus
- US$25: US$2.50 bonus
- US$50: US$5.00 bonus
- US$100: US$10.00 bonus
To add Apple ID Funds, open the App Store, tap your profile picture, then tap Add Funds to Apple ID. The offer is available in the U.S. and other regions.
Further Reading:
[Apple Pay Cash PSA: Be Careful When Carrying a Big Balance]
If you want the maximum $20 bonus, tap the Other line and enter $200. You can only get one bonus during this promotion, so may as well do the most you can!