ganuonglachanh What are you going to do with API? Make a Client App for Phone? And the API Document is not up to date
ganuonglachanh You can try this: https://discuss.flarum.org/d/1925-flagrow-generic-php-api-client-for-flarum-installations
Ralkage @datitisev has supplied docs here since the official API docs are offline: https://datitisev.github.io/FlarumAPIDocs/ You must first understand how API's work and how to properly read API documentation. You can browse around repos from these groups if you want to look into more complex extension development, https://github.com/flagrow/byobu https://gitlab.com/ReFlar/gamification