Today I started receiving the following exception when making callouts to external web services:
System.CalloutException: IO Exception: Server chose TLSv1, but that protocol version is not enabled or not supported by the client.
Why would this start failing?
When connecting to the same org using the Partner API from a client application that doesn't support TLS 1.1 or higher:
UNSUPPORTED_CLIENT: TLS 1.0 has been disabled in this organization. Please use TLS 1.1 or higher when connecting to Salesforce using https.
A POST request for Web-to-lead is intermittently coming back with:
400 Bad Request
StatusDescription: TLS 1.1 or higher required.