Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Are you trying to buy, or trying to renew? Is there any specific error message?
Does your account currently have any subscriptions that are active or about to expire? Check https://account.live.com > subscriptions? If so, if these subscriptions were originally signed up in a different country?
Also, can you go to https://account.live.com > Your info, make sure the language field is not blank or incorrect. Make sure you have it set up to the correct language. Review your country and region as well. Make sure they are correct and matching the credit card's billing address country.
If there's any country mismatch, you typically can run into issue.
If you don't have country mismatch issue, your best bet is to reach out to billing support.
Go to https://support.microsoft.com/contactus, Type "Billing" and press Enter. On the next screen, click "Contact support" at the bottom of the page, then choose "Microsoft 365" > "Manage my subscription". You’ll then see the option to chat with a Microsoft support agent who has access to your account to help review the issue.
You can reference this detail step by step instruction with screenshots I posted in this thread: https://learn.microsoft.com/en-us/answers/c/2714817