Stockouts and overselling are two of the most expensive problems in eCommerce. A stockout means lost sales and potentially lost customers. Overselling means promising something you cannot deliver — leading to cancellations, refunds, and damaged seller metrics on Amazon or Walmart.Both problems stem from the same root cause: inventory data that is not accurate in real time.**The Multi-Channel Inventory Problem**Most eCommerce brands sell on more than one channel. Shopify for DTC, Amazon FBM, Walmart, and maybe wholesale POs all drawing from the same physical inventory. Without a system that updates every channel simultaneously when inventory moves, you are guaranteed to oversell.Here is what typically happens: a brand sells 50 units on Shopify. Their Amazon listing still shows 50 units available because the inventory update has not synced yet. Amazon sells another 20 units. Now they owe 70 units they only have 50 of.**How Real-Time WMS Integration Solves This**A modern warehouse management system (WMS) updates inventory the moment a pick happens. When 3PLCity picks an item for a Shopify order, that unit is immediately removed from available inventory across all connected channels — Amazon, Walmart, Etsy, wholesale — simultaneously. The update happens in seconds, not hours.**Low-Stock Alerts**Real-time inventory also enables proactive low-stock alerts. When a SKU hits a threshold you define — say 50 units — our system sends you an alert so you can reorder before you stockout. You are never surprised by an empty bin.**The Cost of Getting This Wrong**One stockout on your top-selling Amazon listing can cause you to lose your Buy Box and take weeks to recover your ranking. One oversell on Walmart can trigger a seller metric violation. The infrastructure cost of real-time inventory management is far cheaper than these outcomes.