There are many possibilities for your inventory is not get synchroized. Please make sure to check you miss below key steps to support synchronisation.
1. Synchronisation Exception
Connected Inventory only syncs inventory when there is a new order; or when there is a refund order. Other types of activities like 'transfer' , 'edit order' and 'manual update inventory' would not trigger a sync.
. When you change the product (or variant)'s inventory at product admin page, the new inventory will not automatically get synchronised to other products (or variants) in Inventory Group or Bundles and Sets.
You can change the inventory of each product (variant) one by one as usual. However, we recommend to use Bulk Editor to edit multiple products (or variants) on a single screen.
A draft order will not trigger Connected Inventory to synchronise e draft order is converted to an order, synchronisation will happen.
Transfer function in admin page.
Inventory update by other 3rd party app or software.
Shopify's Purchase Order
Shopify Order Editing
Please refers to Article How does Synchronisation Work in Connected Inventory? for more ideas.
2. Enable Tracking Quantity
On Shopify product page, there is an option 'track quantity'. Make sure to enable "Track Quantity" so that Shopify will help to automatically reduce the inventory when a purchase is made. Connected Inventory can sync the inventory accordingly.
3. The product identifier stored in the App is no longer valid
If you have deleted the product, even if you re-create it with the same name again in Shopify, the unique product identifier is changed. You have to modify the Manual Group or Bundle Group manually by deleting the old component and add the new one.
🚀 Pro Tips: Sometimes, the products (variants) do not exist in Shopify but still include in grouping. Sync Inventory will be impacted.
You can find out the deleted the products (variants) from "view inventory history". If you click the products (variants)'s "view inventory history" and below return error page, you need to delete that products(variants) from the grouping. Article Why I see the error showing "The page doesn't exists" ? explains more on this.
4. [For Smart Group / Manual Group] You have not assigned the same initial inventory
Make sure the products under the same group assigned with the same stock level. You can use Bulk Editor to update the initial inventory and make a test order to check your inventory is synced.
5. [For Smart Group] The new products are not included in the Smart Group
If you have create new products or variants, you have to re-scan the SKU in the app.
However, if you have tried all the options, the issue is still not yet resolved, please refer to the Article How to Investigate Stock Movement?.