I have to say buying NFT wasn't that trivial as I was expecting.
First tried purchasing ETH with credit card directly from Metamask (using transak and wyre), both were reject by my bank. Luckily remembered I had an account in a local exchange, sent money there...
... then bought ETH, so I could transfer to my metamask walllet.
Finally transferred to opensea, converted to Polygon (I didn't know about it) so I could be able to purchase the NFT.
Phew, took more than an hour this whole process and not to mention the money that evaporates..