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# Inconsistency for the product (x/y) - The combination/variant has no Main Reference - Amazon Marketplace Plus

## Error: Missing Master Reference

Export log message:

||| Inconsistency for product (x/y) –  
||| Is a Combination/Variant and has no Master Reference

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## Cause

The product sheet does not follow the [catalog structure recommendations](https://doc.common-services.com/en/article/validating-your-catalog-structure-amazon-marketplace-plus-d3xsyp/).  
For a product with combinations, the **master reference** (field "Reference") is missing in the main product sheet.

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## Solution

1. Open the product sheet in PrestaShop.  
2. In the **Information** tab, fill in the **Reference** field (master reference of the product).  
3. Save the product, then re-run the export.

![Master reference on product sheet](https://storage.crisp.chat/users/helpdesk/website/-/3/f/a/8/3fa8ee645cd13200/prestashop-amazon-marketplace-_189z4bc.png)