CreditCardController.php

<?php

// your code
public function index()
{
    try {

        $cards = Card::where('user_id',Auth::user()->id)->orderBy('created_at','desc')->get();
        return $cards; 

    } catch(Exception $e){
        return response()->json(['error' => $e->getMessage()], 500);
    }
}

// Create a repository class in app folder (better if you have another folder), 
// and call it: CreditCardRepository.php

class CreditCardRepository {

  protected $model;
  
  // inject here your Card Model
  public __construct(Card $card) {
    $this->model = $model;
  }
  
  /**
  * Find if the user has a credit card
  */
  public function findCreditCardIfExists(User $user) : bool
  {
    //your User Model should have one to many relationship with Card Model
    return $user->card()->count();
  }
}

// In your controller

// refactor code
public function index()
{
      $creditCardRepository = new CreditCardRepository(new Card);
      $creditCard = $creditCardRepository->findCreditCardIfExists(auth()->user());
  
      if(!$creditCard) {
        return redirect()->url('/');
      }
}