get_page/?id=** returns systematically an error :'not found'

Querying a page via ?get_page&id=** or ?get_page&slug=the-slug-of-the-page
systematically returns an error : {“status”:”error”,”error”:”Not found.”}

I have double-checked that the page exists and is published. And it actually is, it even appears in the result when ?get_page_index is called.

Any idea ? Thanks

https://ww.wp.xz.cn/plugins/json-api/