As discussed in the Link Uphance & Shopify Products (or WooCommerce) Knowledge Articles, you must establish a link between your product and product variants in order to keep the inventory and product details current.  That Knowledge Articles explain how to add these links one product at a time.

Adding these links one product at a time may be cumbersome if you have several product links that need to be added.  To expedite this process and add links for a large number of products, you may opt to use the "Upload eCommerce ID" feature within Uphance.

To use this feature, open Products >> Actions >> Upload eCommerce ID. Download the spreadsheet template, populate it with your data, and upload it again.

After the file is uploaded the products will automatically be connected.  If some products or product variations were not uploaded, you will receive an error message identifying the products.
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