Reading the salesforce documentation it says it can only be used in Production environments:
Why is the probe limited to only production environments?
Release : UIM 20.4 , salesforce probe 2.02
Limitation of WSC connector
The Salesforce probe connectivity to the Salesforce instance is built over the Web Services Connector (WSC) (WSDL-Based APIs) Connector provided by Saleforce. Web Services Connector (WSDL-Based APIs)
The connector does not support Sandbox environments and it only works connected to production environments of salesforce. This is the reason why the probe only supports monitoring production environments.