API: how to fetch streams

[Wajdi-Mabroukeh]

I'm trying to use this api POST /v1/scheduler/sources/discover_schema
to fetch source streams with following body
But it raised me the following error
Could anyone help me with an example since the documentation is poor for this api

    "message": "Invalid json input. Unrecognized field \"sourceId\" (class io.airbyte.api.model.generated.SourceCoreConfig), not marked as ignorable (3 known properties: \"connectionConfiguration\", \"sourceDefinitionId\", \"workspaceId\"])\n at [Source: (org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream); line: 3, column: 16] (through reference chain: io.airbyte.api.model.generated.SourceCoreConfig[\"sourceId\"]) Unrecognized field \"sourceId\" (class io.airbyte.api.model.generated.SourceCoreConfig), not marked as ignorable",
    "exceptionClassName": "com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException",

body

{
   "sourceDefinitionId":"36c891d9-4bd9-43ac-bad2-10e12756272c",
   "sourceId":"defac237-4986-45d2-9e92-7d7ecfd3b4ae",
   "connectionConfiguration":{
      "start_date":"2017-01-25T00:00:00Z",
      "credentials":{
         "client_id":"****",
         "client_secret":"****",
         "refresh_token":"*****",
         "credentials_title":"OAuth Credentials"
      }
   },
   "workspaceId":"4f3fe24e-5ca9-48e8-8191-a2638cd30229"
}

After remove the sourceId, get this error

"message": "Internal Server Error: Cannot invoke \"java.util.UUID.toString()\" because the return value of \"io.airbyte.config.SourceConnection.getSourceId()\" is null",
    "exceptionClassName": "java.lang.NullPointerException",

Should I setup sourceconnection or destination before fetch streams?