Hello there! Thanks for reaching out.
Can you try this process using another browser or Incognito Mode? It might also be worth trying another device or a different internet connection. If you have a Premium subscription, you need to pay with a payment method that matches the country you're currently in. I'd recommend checking out this Support article for more info. Also, can you let me know if you're using a VPN? This could be interfering with things.
Let me know how you get on!