Cakephp 4 Linking 2 existing entities with belongstomany association - authorization

Question

First of all, thank you for your patience. I am getting to grips with PHP coding after a long while. I have finished the famous Cake tutorial and am now continuing with what I know and creating new solutions.
I am creating a voting system. When the current user votes on a suggestion (sames as an article), a new entry needs to be saved in a related cross table between suggestions and users. I thought that the public function link() is the best way to do this. See the function in the ArticlesController below. However, I get an error message "Call to undefined method Authentication\Identity::isNew()". This suggests I have not taken care of some authorization around this call. Can anyone tell me what I missed? Or whether there is a better way to do this?
Note; I do know it looks strange that when I already have my one suggestion I am working through the suggestions table, but I could not find a way for one entity to directly link it to an associated entity (ie I found no link function for entities). It would be nice to hear if this can be done in a leaner way.
public function upvote($id = null)
{
$suggestion = $this->Suggestions->get($id);
$this->Authorization->skipAuthorization();
$user = $this->request->getAttribute('identity');
//Create link between current suggestions and current user in the suggestions_users table
$suggestionsTable = $this->getTableLocator()->get('Suggestions');
$suggestionsTable->Users->link($suggestion,[$user]);
if ($voteTable->save($vote)) {
// The foreign key value was set automatically.
$this->Flash->success(__('Your vote has been cast.'));
}
else {
$this->Flash->error(__('The vote could not be cast. Apologies for the technical issue.'));
}
}
Stack trace;
2020-11-12 13:46:52 Error: [Error] Call to undefined method Authentication\Identity::isNew() in C:\wamp64\www\cake\vendor\cakephp\authorization\src\IdentityDecorator.php on line 125
Stack Trace:
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\ORM\Association\BelongsToMany.php:1323
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\ORM\Association\BelongsToMany.php:864
- C:\wamp64\www\cake\src\Controller\SuggestionsController.php:143
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Controller\Controller.php:529
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Controller\ControllerFactory.php:79
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\BaseApplication.php:251
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:77
- C:\wamp64\www\cake\vendor\cakephp\authorization\src\Middleware\AuthorizationMiddleware.php:129
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\authentication\src\Middleware\AuthenticationMiddleware.php:122
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Routing\Middleware\RoutingMiddleware.php:166
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Middleware\CsrfProtectionMiddleware.php:156
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Middleware\BodyParserMiddleware.php:159
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Routing\Middleware\RoutingMiddleware.php:166
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Routing\Middleware\AssetMiddleware.php:68
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Error\Middleware\ErrorHandlerMiddleware.php:121
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\debug_kit\src\Middleware\DebugKitMiddleware.php:60
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:73
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Runner.php:58
- C:\wamp64\www\cake\vendor\cakephp\cakephp\src\Http\Server.php:90
- C:\wamp64\www\cake\webroot\index.php:40
Request URL: /suggestions/upvote/1
Referer URL: http://localhost:8000/cake/suggestions