def METHOD_NAME(module, client, plan_name: str, selection_name: Union[str, list]):
    result = []
    plan = get_plan_details(module, client, plan_name)
    if not plan:
        module.fail_json(msg=f"The backup plan {plan_name} does not exist. Please create one first.")
    plan_id = plan[0]["backup_plan_id"]
    selection_list = _list_backup_selections(client, module, plan_id)
    if selection_name:
        for selection in selection_list:
            if isinstance(selection_name, list):
                for name in selection_name:
                    if selection["SelectionName"] == name:
                        selection_id = selection["SelectionId"]
                        selection_info = _get_backup_selection(client, module, plan_id, selection_id)
                        result.append(selection_info)
            if isinstance(selection_name, str):
                if selection["SelectionName"] == selection_name:
                    selection_id = selection["SelectionId"]
                    result.append(_get_backup_selection(client, module, plan_id, selection_id))
                    break
    else:
        for selection in selection_list:
            selection_id = selection["SelectionId"]
            result.append(_get_backup_selection(client, module, plan_id, selection_id))
    for v in result:
        if "ResponseMetadata" in v:
            del v["ResponseMetadata"]
        if "BackupSelection" in v:
            for backup_selection_key in v["BackupSelection"]:
                v[backup_selection_key] = v["BackupSelection"][backup_selection_key]
        del v["BackupSelection"]
    return result