Make sure in the add/edit product(s) you have not checked the Disable Woocommerce Sync
If you have multiple locations in DST Systems 1.3, then the location which is assigned to work with WooCommerce from (API settings - Business location) should have the products assigned to it.
Sync will work with Single & variable products only.
Synchronizing products is a time-consuming task and take up to 30 minutes or above depending on the number of products. Do not refresh or leave the page while synchronization is under progress.
Simple & Variable products synchronization is supported.
It has 2 options: