Add item to subscription

Add a new line item to an existing subscription. This is used for multi-product subscriptions where items share the same billing interval.

Related endpoints

• POST /subscriptions — Create a new subscription
• GET /subscriptions — List subscriptions
• GET /subscriptions/{id} — Get subscription by ID
• PATCH /subscriptions/{id} — Update subscription details
• DELETE /subscriptions/{id} — Delete subscription
• POST /subscriptions/{id}/change-plan — Change subscription plan
• POST /subscriptions/{id}/change-quantity — Change subscription quantity
• POST /subscriptions/{id}/preview-renewal — Preview subscription renewal

Common errors

• 400 invalid_request — malformed payload or failed validation.
• 401 unauthenticated — missing, malformed, or revoked API key.
• 404 resource_missing — the referenced resource does not exist or is not visible to your key.

Idempotency

Pass an Idempotency-Key header (UUID v4 recommended) to make retries safe. Keys are valid for 24 hours; see the idempotency guide.

curl -X POST "https://api.revkeen.com/v2/subscriptions/00000000-0000-0000-0000-000000000000/items" \  -H "x-api-key: $REVKEEN_API_KEY" \  -H "Content-Type: application/json" \  -d '{    "product_id": "00000000-0000-0000-0000-000000000000",    "price_id": "00000000-0000-0000-0000-000000000000",    "description": "string",    "quantity": 1,    "currency": "USD",    "unit_amount_minor": 2999,    "fulfillment_type": "none",    "metadata": {}  }'

{
  "data": {
    "id": "550e8400-e29b-41d4-a716-446655440000",
    "subscription_id": "660e8400-e29b-41d4-a716-446655440000",
    "product_id": "770e8400-e29b-41d4-a716-446655440000",
    "price_id": "880e8400-e29b-41d4-a716-446655440000",
    "description": "Pro Plan - Monthly",
    "quantity": 1,
    "currency": "USD",
    "unit_amount_minor": 2999,
    "fulfillment_type": "none",
    "metadata": {
      "property1": null,
      "property2": null
    },
    "created_at": "2024-01-15T10:30:00Z",
    "updated_at": "2024-01-15T10:30:00Z"
  }
}