Flashcard step 2 (add @ApiResource())

App\Entity\Flashcard.php

<?php

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiResource;
// ...

/**
 * @ApiResource()
 * ...
 */
class Flashcard
{
   // ...
}

App\Entity\Lesson.php

<?php

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiResource;
// ...

/**
 * @ApiResource()
 * ...
 */
class Lesson
{
   // ...
}

App\Entity\Subject.php

<?php

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiResource;
// ...

/**
 * @ApiResource()
 * ...
 */
class Subject
{
  // ...
}

App\Entity\User.php

<?php

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiResource;
// ...

/**
 * @ApiResource()
 * ...
 */
class User implements UserInterface
{
   // ...
}