designtopack/public/site/plugins/comments/routes/create.php

<?php

use adrienpayet\comments\Comment;

return [
  'pattern' => '(:all)create-comment.json',
  'method' => 'POST',
  'action'  => function () {
      $json = file_get_contents('php://input');
      $data = json_decode($json);

      $parsedUrl = parse_url($data->dialogUri);
      $query = $parsedUrl['query'] ?? null;
      parse_str($query, $queryParams);
      $stepSlug = $queryParams['dialog'] ?? null;

      $targetPageUri = $stepSlug ? $parsedUrl['path'] . '/' . $stepSlug : $parsedUrl['path'];

      $project = page($parsedUrl['path']);
      $page = page($targetPageUri);
      $file = $page->file($data->fileName);
      $user = kirby()->user($data->userUuid);   

      $comments = $file->comments()->isEmpty() == true ? [] : Yaml::decode($file->comments()->value());

      $commentData = [
        "location" => [
          "page" => $page,
          "project" => $project,
          "dialogUri" => $data->dialogUri,
          "file" => $file
        ],
        "position" => [
          "pageIndex" => $data->position->pageIndex,
          "x" => $data->position->x,
          "y" => $data->position->y
        ],
        "date" => (string) $data->date,
        "text" => $data->text,
        "author" => kirby()->user(),
        "id" => Str::uuid(),
        "type" => "comment",
      ];

      $newComment = new Comment($commentData);

      $comments[] = $newComment->toArray();
      
      $newFile = $file->update([
        'comments' => $comments
      ]);      

      echo json_encode(getFileData($newFile));
      
      try {
        $user->sendNotification($project, $commentData);
      } catch (\Throwable $th) {
        echo json_encode([
          "error" => $th->getMessage() . " in " . $th->getFile() . " line " . $th->getLine(),
        ]);
      }

      exit;
  }
];