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Navigate to Setup > Integrations > Connectors.
Scroll down to the Connector labeled "Marketing Cloud Account Engagement (Pardot)".
Select what account type you are connecting from Live, Demo or Sandbox
Click the “Add Account” button which will take you to the page to enter your Account Engagement (Pardot) credentials.
If you entered the correct credentials, you should see a success message as shown below.
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Now, enter your Business Unit ID. Once done, you’ll see the success prompt as shown here:
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How to find your Account Engagement (Pardot) Business Unit ID?
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