html output

[xfreakart]

Sorry if it is out topic.

I'm struggling with reponses.
I'm able to use :

wp_send_json($output);

But, if I echo something, it goes over the head and the body of the page displays :

OOPS! THAT PAGE CAN’T BE FOUND.

Like if it was an 404 page.

I'm using this lib as plugin for some custom urls:

/players/{slug}

Any clue for what should I be looking for?

[kasztof]

@xfreakart have you found a solution to your problem?