We now pull over the CampaignID (customfield3) into Shipstation. To find your campaign ID go to your campaign and view your url and copy the id after campaigns in the url. Look at the example below, it's 87 in our case.
Next, go to Shipstation and to the filter, "Other "and select the field Customer Field 3 and filter on campaign id 87. Then type this text in "CampaignID:<space><campaign_id>" to filter for orders in that campaign and click Apply.