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  1. Callback Events
  2. SKU Inventory Change Event

The SKU Inventory Change event is sent to your registered webhook endpoint whenever inventory levels change for any SKU. This provides real-time visibility into inventory movements across all locations and statuses.

Use the message_id field to implement idempotent processing and prevent duplicate event handling.

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Event Payload

{
  "callback_url": "https://client.com/api/skuInventoryChange",
  "message_type": "skuInventoryChange",
  "message_id": "e58769ec-c4cf-47f9-b80a-378a9b85aeae",
  "data": [
    {
      "sku_id": "e5d00ff6-b34a-496e-9559-eb90e99463af",
      "customer_identifier": "10000",
      "total_units": 200,
      "total_available_to_sell": 100,
      "as_of": "2018-11-18T00:43:23.095637Z",
      "status_counts": [
        {
          "inventory_location_id": "bf7bb516-ce52-8950-2a8b-9008f0091d93",
          "inventory_location_address": "MasonHub - Rancho Cucamonga | 8595 Milliken Avenue, B102 Rancho Cucamonga, CA 91730",
          "inventory_status": "available",
          "quantity": 100,
          "as_of": "2018-11-18T00:43:22.664965Z"
        }
      ]
    }
  ]
}

​
Payload Fields

callback_url
string

Your registered webhook endpoint URL

message_type
string

Always skuInventoryChange for this event type

message_id
string

Unique identifier for this event. Use for idempotency checks.

data
array

Array of inventory change records. Each record contains:

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Event Triggers

This event is triggered by various inventory operations:

Inbound Receipts

Inventory received from inbound shipments

Order Fulfillment

Inventory allocated or shipped for orders

Adjustments

Manual inventory adjustments and corrections

Returns Processing

Items returned and restocked

Kit Operations

Kit assembly or disassembly operations

Status Changes

Inventory moved between statuses (e.g., QC to available)

​
Implementation Example

Python
@app.route('/api/skuInventoryChange', methods=['POST'])
def handle_inventory_change():
    try:
        payload = request.get_json()
        message_id = payload['message_id']

        # Check if already processed (idempotency)
        if is_message_processed(message_id):
            return 'OK', 200

        # Process each SKU update
        for item in payload['data']:
            sku_id = item['customer_identifier']
            available = item['total_available_to_sell']

            # Update your inventory system
            update_inventory(sku_id, available)

            # Update by location if needed
            for status in item['status_counts']:
                location = status['inventory_location_id']
                quantity = status['quantity']
                status_type = status['inventory_status']

                update_inventory_detail(sku_id, location, status_type, quantity)

        # Mark as processed
        mark_message_processed(message_id)

        return 'OK', 200

    except Exception as e:
        logger.error(f"Inventory webhook error: {e}")
        return 'Error', 500
JavaScript
app.post('/api/skuInventoryChange', async (req, res) => {
  try {
    const payload = req.body;
    const messageId = payload.message_id;

    // Check if already processed (idempotency)
    if (await isMessageProcessed(messageId)) {
      return res.status(200).send('OK');
    }

    // Process each SKU update
    for (const item of payload.data) {
      const skuId = item.customer_identifier;
      const available = item.total_available_to_sell;

      // Update your inventory system
      await updateInventory(skuId, available);

      // Update by location if needed
      for (const status of item.status_counts) {
        await updateInventoryDetail(
          skuId,
          status.inventory_location_id,
          status.inventory_status,
          status.quantity
        );
      }
    }

    // Mark as processed
    await markMessageProcessed(messageId);

    res.status(200).send('OK');

  } catch (error) {
    console.error('Inventory webhook error:', error);
    res.status(500).send('Error');
  }
});

​
Best Practices

Idempotency

Always check message_id to prevent duplicate processing

Fast Response

Return 200 OK quickly, queue heavy processing for background jobs

Error Handling

Return appropriate HTTP status codes for MasonHub retry logic

Logging

Log all events with message_id for debugging and audit trails

High-velocity SKUs may generate frequent events. Implement efficient processing and consider batching database updates.

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Response Requirements

Your webhook endpoint must:

  1. Respond within 30 seconds - Return HTTP 200 to acknowledge receipt
  2. Use proper status codes:
    • 200 - Event processed successfully
    • 500 - Processing error (MasonHub will retry)
  3. Handle retries - MasonHub will retry failed webhooks with exponential backoff
  4. Validate payload - Verify the payload structure before processing

​
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