ActiveCampaign: Using resource "Campaign Report Open List"
When you create a data source using the resource 'Campaign Report Open List' you will need to use the date dimensions 'tstamp' and 'tstamp_iso'.
It also required the use of a parameter for the 'campaign id' there are several ways to obtain a campaign id, the easiest is to login to your ActiveCampaign account and grab the 'campaign id' from the URL as per the screen shot below. This resource is from the ActiveCampaign API v1, which is an older version. (There are no plans to sunset the API v1 and any removal would be notified by ActiveCampaign)