If when clicking the Synchronize button you see the following error:
Error while executing the method aemListContent' of service 'nms:delivery'
To fix this issue, make sure the AEM connection-url configured in the External Accounts is reachable from the machine.
A switch from localhost to an IP-address solved this issue.
Link:- https://docs.adobe.com/docs/en/aem/6-1/administer/integration/marketing-cloud/campaign/campaignonpre...
I hope this will help you.
Thanks and Regards
Kautuk Sahni