Migrations can have more than one journalid. You can find the journalid in the response of a results list for a specific migration id.

In this request, we searched for results for the migration with the id 16. 
<your_control_room_url>/v3/migration/16/results/list
The request returned the id in each object list as the journalid. In this example, there are two journal identifiers, 30 and 31, for the migration id 16.
{
    "page": {
        "offset": 0,
        "total": 2,
        "totalFilter": 2
    },
    "list": [
        {
            "sourceId": 12,
            "sourceName": "Dependency of IGN-23437.mbot",
            "sourcePath": "Automation Anywhere\\Bots\\My MetaBots\\Dependency of IGN-23437.mbot",
            "sourceType": "application/vnd.aa.mbot",
            "targetId": 0,
            "status": "FAILED",
            "reason": "The logic IGN-23437 has some commands or actions which are not yet supported for migration.",
            "selectedByUser": true,
            "userId": 9,
            "id": 30,
            "targetName": "",
            "targetPath": "",
            "targetType": ""
        },
        {
            "sourceId": 12,
            "sourceName": "Dependency of IGN-23437.mbot",
            "sourcePath": "Automation Anywhere\\Bots\\My MetaBots\\Dependency of IGN-23437.mbot",
            "sourceType": "application/vnd.aa.mbot",
            "targetId": 0,
            "status": "FAILED",
            "reason": "Migration of MetaBot failed.",
            "selectedByUser": false,
            "userId": 9,
            "id": 31,
            "targetName": "",
            "targetPath": "",
            "targetType": ""
        }
    ]
}
You can use the migration id and journal id in an action mapping request.
<your_control_room_url>/v3/migration/16/journal/31/actionmappings/list