Dose apple provide 'Apple Gift Card' in singapore?

but I don't have a valid payment method for it.

You need to have a valid payment method, see -> Add a payment method to your Apple ID

Add a payment method to your Apple ID – Apple Support (UK)

See also  ⤵️

Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

App Store & iTunes gift card: Apple Gift Card - Apple (UK)

• Add money to your Apple Account balance anytime, no gift card needed.

Buy Apple Gift Card -> Buy Apple Gift Cards - Apple

See also this Apple article:  If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

• You can't redeem Apple Gift Cards or App Store & iTunes Gift Cards outside the country or region of purchase. For example, if you bought an App Store & iTunes Gift Card in France, you can't redeem it in the App Store in the United States.

If you update your payment method or add funds to your Apple ID balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.

Get help and assistant from Apple directly, see -> Singapore

Or call:

Within Singapore -> 800-186-1087

Outside Singapore -> (65) 6972-51711