BigCommerce inventory updates need the product_id, not just the SKU

When updating BigCommerce inventorylevel, first resolve each SKU to its productid with a GET on the products collection. The inventory write itself must target the product_id. Cache the SKU-to-ID mapping in your script so you are not re-listing the catalog on every sync run.

Context: Stack Overflow #19273118 (accepted answer, 4 votes): the asker tried to PUT inventorylevel using only the product SKU and it silently failed. The accepted answer confirms there is no update-by-SKU path: you must reference the productid. The workaround used in practice is to list all products once, build a sku-to-productid map, then issue the inventory PUT against the resolved productid.