Syncing existing Campaigns from your Email Marketing Automation software such as Constant Contact, Mailchimp, Act-On, Drip, Klaviyo, others to existing CRM Campaigns is not supported.
The way it works is simple. You can send multiple Email Campaigns to 1 List in your Marketing Automation software so SyncApps create a tracking campaign to track all metrics. The Campaign created by anyone in CRM is just that, a Campaign that will create a List, Group or Segment.
If using Campaign a List feature in SyncApps then each Campaign needs to be created first in CRM to sync with your Marketing Automation software as Lists, Groups or Segments. After that, any email Campaign sent to these Lists, Groups or Segments will create a CRM Campaign of the same name as the email and track all the Campaign metrics from your Marketing Automation Software back to the CRM Campaign.
Please also note that CRM record data is synced from your Email Marketing Automation only if the email address doesn't exist in CRM at the time of syncing. An exception to this rule is Mailchimp and others which use webhooks to update existing CRM record data.