In order to sync products follow these guidelines:
1. Match products already created in WooCommerce with products in iZettle
Click the Match Products button. The integration will list products in WooCommerce by SKU. If there is a matching SKU in iZettle it will connect these products and enable future syncing.
2. Sync products from WooCommerce to iZettle
Go to WooCommerce -> iZettle and select the Products tab. Underneath Sync products you will have two options: either select specific products for synchronisation to iZettle or a full sync of all products. If the product has not been matched to an existing product in iZettle it will create a new product.
This sync will not look for names nor SKUs, it will only consider previously connected products such as in step 1, or products created in WooCommerce and already synced (and hence matched to a newly created product in iZettle) in this step. If the product being synced has a connected product in iZettle, this product will be updated. All other cases will lead to creating a new product in iZettle, hence possibly creating unwanted duplicates!
3. Export products from iZettle to WooCommerce
Make an export in iZettle of the products missing in WooCommerce. Pay attention to the fact that all products must have an SKU in iZettle. Then import the export file with the import tool of your choice (e.g http://www.wpallimport.com/ with the Woocommerce addon) to WooCommerce.
After importing, follow step 1 to match these products with iZettle, or duplicates will occur when syncing!