php curl json post

    if ( !empty( $problems ) ) {

        $json = json_encode( $problems );

        $url = 'http://en.lichess.org/api/problem?token=';

        $ch = curl_init( $url );
        curl_setopt( $ch, CURLOPT_POST, 1 );
        curl_setopt( $ch, CURLOPT_POSTFIELDS, $json );
        curl_setopt( $ch, CURLOPT_FOLLOWLOCATION, 1 );
        curl_setopt( $ch, CURLOPT_HEADER, 0 );
        curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1 );

        $response = curl_exec( $ch );

        print_r( $response );

        return $json;

    } else {

        exit( 1 );

    }