How to fix the “Missing Value [Tax]” Error of Google Merchant Center?
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You need to check if there is sales tax created and enabled in your merchant center account or not. If not, you may go to your Google merchant center account → Settings → Sales tax → create your tax settings. This option is valid only for the US. Or,
You may also sync tax from the application using one click. Follow the below steps: Go to the Merchant Center section in Application → Settings → Click on Start Syncing under the Tax Section