Laravel Passport wrong expires in date

i am getting wrong expire in date, not sure why

"expires_in": "1970-01-01 23:59:59"

in my AuthServiceProvider i have this code

public function boot()
    {
        $this->registerPolicies();

        Passport::routes(function ($router) {
            $router->forAccessTokens();
            $router->forPersonalAccessTokens();
            $router->forTransientTokens();
        });
        Passport::tokensExpireIn(now()->addDay());
        Passport::refreshTokensExpireIn(now()->addDays(10));
    }

this is how i am getting it

'expires_in' => Carbon::parse($results->expires_in)->toDateTimeString(),