xml-rpc does not turn on

I want to use my Android app to update my blog.
I have many wordpress blogs on my hosting server and I have blogs where I have been able to just tick the box and connect with my app.
I however, have one blog, that when I tick the box and click save, it looks like it’s saving the setting, but it doesn’t.
No error, no tick, and no functionality with my Android app.

Any ideas for a work around or why this might be?