To select or clear a field type of "checkbox" in Pardot, reference the field with fieldname and underscore 0 . To clear a checkbox set fieldname to an empty string, and to select it set it to the name of the field.
In this example, your custom field is called customfield and your check box is called Testbox.
To select it, use {"customfield_0":"Testbox"}.
To clear it, use {"customfield_0":""}.
Pardot only supports searching activities by certain criteria - users can query by created_after or created_before (e.g. today, yesterday, last_7_days, this_month, last_month, ), id_greater_than, id_less_than, prospect_only, or type.
For more information see http://developer.pardot.com/kb/api-version-3/visitor-activities/#supported-search-criteria.
There can be other reasons why an authenticated instance cannot retrieve data, but the first configuration to confirm in this case is the "Pardot API Version" setup in the connector instance. This version currently defaults to '3' in the 'Optional Fields' when an instance is created, and this value should not be changed unless the associated Pardot account has version 4 enabled.
In Pardot under Settings->Account if the feature is disabled for "Allow Multiple Prospects with the Same Email Address" then the account can only use Pardot API version 3.
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