Here are main things you need to know about product sync:
The app automatically syncs products
You cannot manually trigger a product sync
A product sync is triggered automatically when you open the app
The app looks for new or updated products when it syncs products
If no additions or edits are made to your products since the last time you opened the app, products won't be synced.
Product Sync is only required to be completed to be able to use the Manage Products part of the app ( creating new product groups, assigning products to group )
When the app sees a product's fulfillment service has changed, it will show that product in the Default group of that fulfillment service.
Key Takeaway: You should not worry about product sync! Just know that it needs to be completed before you manage product group assignments.
Deeper Dive: What the product sync is used for
In order to allow you to create product groups and assign products to groups, the app must first know what all the products in the shop are to be able to display those products in the Manage Products page.
When the app syncs products, it looks for two things: any new products added since the app was last opened, and any updated products whose fulfillment service may have changed.
When the app see a new product added, it will show that product as belonging the the Default group of the fulfillment service it is assigned to.
When the app sees and updated product, it will check to see if it's fulfillment service has changed. If the product's fulfillment service has not changed, it leave the product as it is. If the product's fulfillment service has changed, we will update it so that that product is now showing as belonging to the Default group of the fulfillment service it has been newly assigned to.