miz_jim
You need to be on the Desktop or Mobile site.
If you are on a computer: https://www.webnovel.com
If you are on a phone: https://m.webnovel.com
Open the site. Login. Click (mobile) or Hover (computer) over your profile picture and you should see a button that says Get More next to your number of coins. Click on that and you will be able to buy using Paypal.