For the embedder app to be able to work within a given Confluence space, it needs to have at least the ‘view’ permission on the space.
If the permission is not granted, you may see a proper error message or in some rare cases the page won’t load. Just grant the permission as explained below & the app will be back to what it does best.
You have to be an admin on the Confluence space to manage its permissions.
To manage permissions:
Go to (Settings) in the Confluence navigation.
Click Space Permissions.
Locate the space in the Individual Spaces list, and click Manage Permissions.
Edit Individual Users permissions and add app user(amoeboids.embedder) in text box.
Add app user and give view permission to it.
Save the changes by clicking Save all button at bottom.