FAS Server fails to register with the Citrix Cloud.

Exception: System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host

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You can test connectivity on the FAS server using Cloud Connector Check utility as an administrator.

You can also add the listed URLs to the trusted sites on the FAS server by clicking on 'Add Citrix Trusted Sites' in the Cloud Connector Check utility.

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Problem Cause

Connectivity issue between FAS server and Citrix Cloud.

https://docs.citrix.com/en-us/federated-authentication-service/current-release/config-manage/security.html#connections-between-citrix-federated-authentication-service-and-citrix-cloud
 

The console and FAS access the following addresses using the user’s account and the Network Service account respectively.

• FAS administration console, under the user’s account
  • *.cloud.com
  • *.citrixworkspacesapi.net
  • Addresses required by a third party identity provider, if one is used in your environment
• FAS service, under the Network Service account:
  • *.citrixworkspacesapi.net
  • *.citrixnetworkapi.net

If your environment includes proxy servers, configure the user proxy with the addresses for the FAS administration console. Also, ensure that the address for the Network Service account is configured using netsh or a similar tool.