Does anyone know what is the cause of the next error on the author instance
com.day.cq.mcm.campaign.servlets.CampaignMetaDataServlet Could not connect to Adobe Campaign
com.day.cq.mcm.campaign.ConnectionException: Unexpected status code (expected 200, was 404
I believe it is a 2-way connection and The Campaign server should be able to find AEM instance on the internet if using Campaign server on cloud. If you are trying a local setup, try externalizing the AEM instance by using ngrok.
Also, try using AEM admin user to connect to Campaign and let me know if that works.
A Campaign server uses OOTB AEM campaign-remote user. Note that by default it does not have a password. You need to set it up.
AEM Campaign cloud configuration requires aemserver user, that needs to be configured on the campaign server.
You can also check step-by-step integration KB available at: