trouble with adding payment method

Thank you, exists the possibility that the servers are still processing your recent account region change.

Usually can take up to 72 hours to see the changes everywhere.
Try waiting this time and then add the payment method one more time from here:
https://account.microsoft.com/billing/payments

Make sure to select "Singapore" under "For purchases in"

If maybe the issue persist double check if your preferred billing address is the same as the one in your bank statement
https://account.microsoft.com/billing/addresses

Do you have a billing violation on your account? You can check by going to
https://billing.microsoft.com or calling phone support in your region.

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this GUNDAMPILOTO

Where are you physically located? (Country)
And, your Microsoft account region and payment method are the same as your physical location?

Double check your account region here: https://account.microsoft.com/profile

PS: Please be honest, this is extremely important

Thank you for your reply JOSEFLBOHORQUEZ . I have checked my account and it has been changed to the United Kingdom . Despite changing the region back to my home country , the issue still persists indefinitely . I have double checked my credentials

I have the same problem, but with my e-card i create for a single purchase. Have always been working but not anymore, I dont know if its my bank or if its xbox market, but i am frustrated i want to buy! =)