On 2016, i build a ios and android app use ionic 1 and wordpress 4.3.10 with plugin wp-rest-api 1.0, which working perfectly, until now still working good.
In local, i make a test recently, upgrade wordpress to latest version, and i test ionic app on local using browser, seem like it broke. unable to get any data from wordpress.
After few hour working around, it seem like latest version of wordpress is not support wp-rest-api 1.0 any more, reason is they merge this plugin to wordpress core, that’s mean wp-rest-api 2.0 and wordpress now they are together.
i am using this site as example, etenbo.com using latest wordpress version so if you type on url http://etenbo.com/wp-json/ you can see all the json data. i don’t have any rest api install on this site, but still can get the site json data. If you know how to use rest api 2.0, you may familiar with wordpress json core.
here is documentation for rest api 2.0