Layer seems to be an internal network and are not accessible to ArcGIS.com. Thus, editing will be disabled on these layers

Error Message

When attempting to add feature services to either Portal for ArcGIS or ArcGIS Online, the following error occurs:

Error:   
Layer seems to be an internal network and are not accessible to ArcGIS.com. Thus, editing will be disabled on these layers.

Cause

There are several potential causes for this error.

• The user added the service to ArcGIS Online using the Web Adaptor URL. If the server hosting the app falls on a different domain hosted by ArcGIS Web Adaptor than the service hosted by the GIS server, the web browser plug-in running the web app is not allowed to access the service, due to security reasons. For more information, refer to ArcGIS Server: Common problems and solutions.
• A known limitation of Internet Explorer (IE) 10 and earlier, due to cross-origin resource sharing (CORS).
• The service is secured with web-tier authentication to Portal for ArcGIS and is not federated with the service from the server. Editing feature services secured with web-tier authentication requires a web browser enabled with CORS. For more information, refer to the following link, ArcGIS Online Help: Configure security settings.

Solution or Workaround

Depending on the expected cause, use one or more of the solutions below to solve this issue.

Note:
The Trusted Servers option is only supported in Portal for ArcGIS 10.4 and later.

Note:
If using ArcGIS Online, the option to use trusted servers is the only required option. For more information, refer to ArcGIS Online Help: Configure security settings.