Previously functional connections from external resources, such as Web API calls, to Appian Cloud instances start failing with the following exception or a similar one indicating the forceful termination of the connection to Appian:
The underlying connection was closed: An unexpected error occurred on a send.
This typically indicates that the resource attempting to connect to the Appian Cloud instance is not configured to use TLS 1.1 or higher. Appian does not support TLS 1.0.
Use cURL or a third-party tool such as Postman or SoapUI from the origin server to verify that the connection still works as expected with a client that supports TLS 1.1. If this is the case, update the application code or client version to support TLS 1.1 or higher. Please note that Appian is unable to provide detailed instructions for updating external systems to use TLS 1.1. If you require assistance in making this change, contact the vendor or developer supplying the external system.
This article applies to all versions of Appian Cloud.
Last Reviewed: July 2018