Error while publishing content from Sandbox AEM to Edge delivery Services

Hi Team,

I'm trying to setup Universal Editor and EDS with AEM sandbox following this tutorial https://experienceleague.adobe.com/en/docs/experience-manager-cloud-service/content/edge-delivery/wysiwyg-authoring/edge-dev-getting-started 

Unfortunately I'm not able to see the result on https://main--<repository-name>--<owner>.aem.page or https://main--<repository-name>--<owner>.aem.live, because I'm getting a 404 error on both of those URLs. 

The problem seems to be with publishing as I'm getting an error in the replication log, that my sandbox dev author is 'internal or unknown'

Is it not possible to use a sandbox environment to try out wysiwyg authoring with EDS?

Thanks for your support and regards.