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The error message says that given attribute is missing in Product Flat Calalog and thus is not available for the product export process.

Solution

Automated one-click solution

Just click on the link Add the attribute(s) to Product Flat Catalog dispalyed in the error message and execute profile again:

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Manual solution

Step #1 - Enable Flat Catalog

Koongo Connector uses Flat Product and Flat Category data, so please make sure you have enabled these two settings. You can enable Flat by clicking on the link in the note or navigate to Stores -> Settings -> Configuration → System → Catalog → Storefront:

• Use Flat Catalog Category = Yes
• Use Flat Catalog Product = Yes

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Step #2 - Check Product Attribute Detail

Navigate to the attribute's detail in Stores → Attributes → Product.  

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Then, set the option Use in Product Listing to Yes and save attribute details:

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Step #3 - Reindex Product Index

If your server cron job runs properly, Product and Category Flat Catalog will be reindexed automatically.

You can force reindex via ssh by following command in your Magento 2 installation folder:

php bin/magento indexer:reindex

Step #4 - Flush Cache Storage

Click Flush Cache Storage button under System → Tools → Cache Management:

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