Hi, my name is Ric. Please make sure that your Microsoft Store app is updated and that you are signed in on your correct Microsoft Account. Clear the Store cache by pressing Win + R, type wsreset.exe and press enter. If you’re using a browser for payment authentication, try switching to another browser or device. Check if your card provider has additional security requirements like an SMS verification or app approval. Can you try purchasing through this link https://apps.microsoft.com/detail/9n4wgh0z6vhq?hl=en-GB&gl=PH.
Hope this helps.