Thanks for your help! It fixes the 400 error now by adding back the Subject tag and clear the OrganizationState value (as we're outside US).
But I encounter 404 error now. Is it correct to do a PUT to, say in previous example, https://api.constantcontact.com/ws/customers/myaccount/campaigns/1103756094823. Anyway, I tried both http and https with the same error.
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