Over the last 24 hours, the service ArcGIS StoryMaps uses to validate embed links has been experiencing technical issues. These issues prevent story authors from adding new embeds to a story and may affect embed card details in the builder. Other aspects of the builder should not be affected, nor should your published stories that already contain embeds.
Once the service is back up, story authoring will return to normal. Please try again later.
A fix for the issues has been implemented and the provider is monitoring the results. Our testing shows that embed links are now working again in ArcGIS StoryMaps. We'll continue to monitor the situation and post updates here if needed.