src/Operations.php
public function comment(string $parent_author, string $parent_permlink, string $author, string $permlink, string $body, string $app = '')
    {
        $permlink  = Helpers::limit($permlink, 35);
        $permalink = Helpers::slug($permlink).'-'.time();
        $metadata  = [];

        if (!empty($app))
        {
            $metadata['app'] = $app;
        }

        $metadata  = json_encode($metadata);
        $request   = [
            'operations' =>
                [
                    [
                        'comment',
                        [
                            'parent_author'   => $parent_author,
                            'parent_permlink' => $parent_permlink,
                            'author'          => $author,
                            'permlink'        => $permalink,
                            'title'           => '',
                            'body'            => $body,
                            'json_metadata'   => empty($metadata) ? '' : $metadata
                        ]
                    ]
                ]
        ];

        return $request;
    }
public function comment(string $parent_author, string $parent_permlink, string $author, string $permlink, string $body, string $app = '')
    {
        $permlink  = Helpers::limit($permlink, 35);
        $permalink = Helpers::slug($permlink).'-'.time();
        $metadata  = [];

        if (!empty($app))
        {
            $metadata['app'] = $app;
        }

        $metadata  = json_encode($metadata);
        $request   = [
            'operations' =>
                [
                    [
                        'comment',
                        [
                            'parent_author'   => $parent_author,
                            'parent_permlink' => $parent_permlink,
                            'author'          => $author,
                            'permlink'        => $permalink,
                            'title'           => '',
                            'body'            => $body,
                            'json_metadata'   => empty($metadata) ? '' : $metadata
                        ]
                    ]
                ]
        ];

        return $request;
    }
New comment

@param string $parent_author   Original poster or "parent author"
@param string $parent_permlink Original post permalink or "parent permalink"
@param string $author          The author who is posting
@param string $permlink        Permalink for the comment
@param string $body            Body of the post
@param string $app             Name of the application in use for the post
@return array