getFirstMediaUrl returns null in laravel resource observer created method

[fredchess]

Hello, I'm using Images field to attach an image to a resource. After the resource created I want to created associated product in Stripe.
To do this I have created an resource Observer but when I want to retrieve image from resource using getFirstMediaUrl(), this returns null.

This is my observer:

class FormuleObserver implements ShouldHandleEventsAfterCommit
{
public function __construct(public StripeClient $stripeClient)
{

}

public function saved(Formule $formule): void
{
    try {
        $product = $this->stripeClient->products->create(
            [
                'name' => $formule->name,
                'description' => $formule->mini_description,
                'default_price_data' => [
                    'currency' => 'EUR',
                    'unit_amount' => $formule->price * 100,
                ],
                'images' => [
                    $formule->getFirstMediaUrl('formule_images')
                ]
            ]
        );

        $formule->update([
            'stripe_product_id' => $product['id']
        ]);
    } catch (Exception $e) {
        error_log($e->getMessage());
        error_log($formule->getFirstMediaUrl('formule_images'));
        $formule->delete();
    }
}

}