// config/subscribd.php
'plans' => [
    'api_tiered' => [
        'name'           => 'API (Tiered)',
        'rule'           => 'tiered',
        'amount'         => 0,           // base price; tier amounts drive the bill
        'currency'       => 'USD',
        'interval'       => 'month',
        'interval_count' => 1,
        'rule_config'    => [
            'tiers' => [
                // up_to: null means "remainder / infinite"
                ['up_to' =>  1000, 'unit_amount' => 5,  'flat_amount' =>     0],
                ['up_to' => 10000, 'unit_amount' => 3,  'flat_amount' =>  2000],
                ['up_to' =>  null, 'unit_amount' => 1,  'flat_amount' =>  5000],
            ],
        ],
        'features' => ['api_calls' => null],
    ],
],

use Pixelworxio\Subscribd\Actions\RecordUsage;

app(RecordUsage::class)->execute(
    $subscription->items->firstWhere('key', 'api_calls'),
    $callsThisBatch,
    idempotencyKey: $requestId,
);

use Pixelworxio\Subscribd\Actions\CreateSubscription;
use Pixelworxio\Subscribd\Models\Plan;

$plan = Plan::query()->where('key', 'api_tiered')->firstOrFail();

app(CreateSubscription::class)->execute($user, $plan);