How to add apple payment method?

Hello all,

I'm new to Mac and iCloud and will appreciate if someone can help me with the payment methods.

When I first set my account, I chose "Not now" when I got to the payment method part, thinking I can do it later. But now when I log into my account settings and go to payment methods, I'm unable to add or delete anything. I'm just getting a cryptic error:

I found some people mentioning using the store or iTunes to do it, but I couldn't sign in using my iCloud account. It is in some kind of weird signing in loop.

Clicking "Review" will send me back to sign in popup.

I have no clue what the **** is going on here, can someone tell me what I should do now?

Thanks