Shopify was unable to create the variant (Product X) because one or more of its properties is a duplicate of an existing variant of the product at (URL). Please check (Product X) in LightSpeed and uncheck 'Sell on WebStore' in order to avoid future errors.
This error means that a Variant with the same options already exists in Shopify.
Shopify prevents duplicate Variants from being created. Channels will attempt to update the mapping when this error is received. If the error persists, you may delete the Variant from Shopify and Channels will republish it and be able to update it moving forward.
If the product is not a true duplicate of a previously created product, adjustments will need to be made to the product in point of sale to ensure it is unique in order to push into Shopify.