Web Monetization as provided by Coil (http://coil.com) functions as a $5/month subscription where the money a subscriber pays gets divided between the WM enabled content that is used/played during each month.
Technical information here: https://itch.io/jam/the-web-monetization-challenge-2020/topic/1047889/about-web-...
In order for you as a developer to test and experiment with Web Monetization it is recommended that you have a subscription of your own. We gave away a free month with Coil at the beginning of the jam:
https://itch.io/jam/the-web-monetization-challenge-2020/topic/1031845/free-one-m...
If you send an email to the address mentioned in the above post we'll provide a one month voucher.
As an alternative you can use this browser extension to simulate Web Monetization on localhost:
https://dev.to/gustavogr/web-monetization-simulator-dnc
Finally, if you do not register with Coil and set up a payment pointer using a wallet provider you can use the Defold Foundation pointer in your submitted game:
<meta name="monetization" content="$ilp.uphold.com/QkG86UgXzKq8">