SellerSKU is a unique alpha-numerical value assigned to each of your Amazon products and variants.

In order to search by this unique identifier in Synccentric, you must have your SP-API keys in your Synccentric campaign. To do this, authorize the Synccentric app with your Amazon Seller Central account from your Campaign settings in Synccentric.

If you're trying to search by 'SKU' (not sellerSKU), import your identifiers as 'MPN' which will search related fields on Amazon.