This Work:

  sla:notification-msg>HI</sla:notification-msg>

This Work, Also:

   Properties: HI=Hello

   sla:notification-msg>${HI}</sla:notification-msg>

This NOT Works:

  sla:notification-msg>${wf:actionData('Java01')['output']}</sla:notification-msg>

  Error Formating XML in workflow

  Eror: E0803: IO error, E1004: Expression language evaluation error, Validation error :No function is mapped to the name "wf:actionData"

Note: ${wf:actionData('Java01')['output']}, runs OK because I use in a Decisition / switch later