The error you're seeing is quite specific: the source system you're trying to connect to either:
- Does not have SSL/TLS enabled.
- Or, it has SSL enabled but it's using a version lower than TLS 1.2 which your application (Azure Synapse Analytics or Azure Data Factory) is expecting.
Given that you said you tested the connection manually and it worked fine, the issue seems to be intermittent or related to how the automated connection is initiated.
Make sure that the source system indeed has SSL enabled and is using TLS 1.2 or higher. If it's a database, you might need to consult its documentation or work with your system administrator.
Sometimes, the way the connection string is formatted or the parameters included can cause issues. Make sure the connection string used in your pipeline matches the one you're using manually.
If you're using a Service Principal for the pipeline, ensure it has the necessary permissions to the source system and that its credentials haven't expired.
It's possible for transient network issues to cause these kinds of errors. Though, if this is the cause, the error would be intermittent.