Hello Alvin,
Welcome to the Apple Support Communities. You'd like to know what payment methods can be used to add funds to your Apple ID.
If this is correct, this article will provide you with the payment methods which you can use in your region: Payment methods that you can use with your Apple ID. The payment method will need to match your billing address for your Apple ID as well.
Be sure you have checked the following items as listed in the If your iCloud Contacts, Calendars, or Reminders won’t sync article:
"1 - Check the system status of iCloud Contacts, Calendars, and Reminders.
2 - If a reminder isn't showing up on some devices, make sure that you're running the latest iOS, iPadOS, or macOS on each device. Upgraded reminders and shared reminders in iOS 13 or later or macOS Catalina or later aren't compatible with earlier versions of iOS or macOS. Learn more.
3 - Make sure that the date and time settings on your iPhone, iPad, iPod touch, Mac, or PC are correct.
4 - Make sure that you're signed in to iCloud with the same Apple ID on all of your devices. Then, check that you turned on Contacts, Calendars, and Reminders* in your iCloud settings.
5 - Check your Internet connection. Open Safari and go to www.apple.com. If you can’t open the page, learn what to do.
6 - Check that you can access secure websites. Open Safari and go to your Apple ID account page. If the website won't open, contact your Internet service provider for help.
7 - Make sure that you haven't exceeded your iCloud storage limit or the storage limits for iCloud Contacts, Calendars, and Reminders."
Once you have worked through those 7 steps, and you have verified that both devices are signed in with the same Apple ID in iCloud restart both devices and see if there is any change.
If you find you need more assistance, you can contact Apple Support here: Get Support.
All the best.