Error 500 json request on php but not on Browser

I’m using kirby provides the content via json
e.g.: “domain.com/kirby/folio” - returns a folio json obj
that works very well when the frontend requests it, or if I type that url on the browser

but it fails (error 500) if I try to use it on a php file:
e.g: make the request on my domain.com/index.php, using:
file_get_contents(domain.com/kirby/folio)

any idea why?

Maybe this SO answer helps: http://stackoverflow.com/questions/10524748/why-im-getting-500-error-when-using-file-get-contents-but-works-in-a-browser

http://php.net/manual/de/function.stream-context-create.php