When a variant reaches Google without the identifier data you expected, separate two questions: is the identifier actually present and consistent in Shopify, or is the downstream feed/sync failing to carry it? PAL Catalog Check helps with the first question.
Install PAL Catalog Check — FreeAudit a CSV instead
Identifier problems often hide at variant level. Confirm the affected variant has the SKU/MPN or barcode/GTIN you intended to submit.
Use manufacturer-assigned identifiers when they exist. Google’s product-data guidance says not to guess or manufacture an MPN or GTIN.
Review title, vendor/brand, product URL, images, price and variant structure. A feed problem can be compounded by more than one catalog-readiness issue.
If Shopify contains the correct identifier on the exact variant but Merchant Center still receives a blank or different value, the remaining problem may be in the feed mapping, channel app, supplemental source or sync path. PAL does not diagnose Merchant Center transport or account-side configuration.
What it cannot prove: that Google received the field, that a particular feed mapping is correct, or that Merchant Center will approve the product.
PAL Catalog Check is read-only and requests product access for catalog scanning. The Free plan checks the current Shopify catalog and gives remediation guidance without editing products or requiring Google Merchant Center credentials.
PAL is not affiliated with Google. Always verify final diagnostics in Shopify and Merchant Center.