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Using Grid Custom Actions in a Salesforce Community
To use Grid custom actions in a Salesforce Community, you must disable content sniffing. When content sniffing is not disabled custom actions will not show on Conga Grid and you receive an error when you try to use a custom action.
To enable custom actions in a Salesforce Community:
Click the Salesforce setup Icon
Search for All Sites in the Quick Find search box
Select the builder for the community you want to edit
Click the community menu icon in the top left corner