I have a problem while adding fund in my Apple ID

See Add funds to your Apple ID https://support.apple.com/en-us/HT208687

"Before you can add funds to your Apple ID, you must have a valid payment method on file. Learn about the payment methods that you can use with your Apple ID. ... See how to Add funds to your Apple ID https://support.apple.com/en-us/HT208687  Note that "after you authorize the payment, the funds ... [are credited] to your Apple ID. Then, you can use the credit to make purchases from the App Store or iTunes store. Need more help? Contact Apple support for help here: Get started."

Also you can get Apple telephone support for help in solving your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362 Be patient sometimes Apple support is closed to immediate phone support.

Apple ID Support -

https://support.apple.com/apple-id

World-wide Apple Support -

https://support.apple.com/en-us/HT204169

Support by phone, email or chat -

https://getsupport.apple.com/

Apple Support by Twitter -

https://twitter.com/AppleSupport

ASC - Late 2012 Mac mini, macOS 10.15.4; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.4.1; iPhone 8+, iOS 13.4.1; TV 4th Gen, tvOS 13.4;  HomePods, audioOS 13.4 and Airport Express w/ Airplay 2