To pay for your subscription:
Some mobile providers may offer the ability to pay through your plan. If you do not see the option to pay through your mobile provider, check this article for possible solutions for this problem. For more information on accepted Google Play Payment methods, see here.
After paying, it may take 3-5 days for your payment to be processed. You will then see your subscription extended for either 1 year, 3 years or 5 years, depending on the option you chose.
If you want a detailed description of the payment options, take a look at What payment options do I have?
Cheers,
WhatsApp Support Team