This error means Shopify is refusing a request because SKULabs doesn't have the permission it needs on your store. You may also see it as ACCESS_DENIED or "access denied. Please re-authenticate your store" in Sync Reports.
Common causes
SKULabs added a feature that needs a new permission after your store was connected. For example, Shopify returns sync needs access to returns, so stores connected before it was released must reauthorize.
The SKULabs app's access was removed or changed in your Shopify admin.
The person who authorized SKULabs didn't have permission in Shopify to approve all of the access SKULabs asks for.
How to fix it
In SKULabs, go to Settings > Stores and open your Shopify store.
Open the Access credentials & integration settings panel.
Click Authorize SKULabs.
Sign in to Shopify as the store owner (or a staff account with permission to manage apps) and approve the requested access.
Back in SKULabs, run the sync that failed again (for example, order or listings sync) and check Sync Reports.
If the error continues after reauthorizing, contact SKULabs support with the store name and the exact error from Sync Reports.
Related: Shopify Returns Sync