Need help with dataweave map function

Hi Guys,

I am unable to transform the below input payload in json to expected output.

Input:

[
   {
      "bea_order":[
      ]
   },
   {
      "bea_order":[
         {
            "PO_Receipt_Date__c":"2021-08-13",
            "Id":"a3I1T000003E6SQUA0"
         },
         {
            "PO_Receipt_Date__c":null,
            "Id":"a3Iq0000000OhnREAS"
         },
         {
            "PO_Receipt_Date__c":null,
            "Id":"a3Iq0000000OhnWEAS"
         }
      ]
   },
   {
      "bea_order":[
         {
            "PO_Receipt_Date__c":"2022-05-06",
            "Id":"a3I1T000003E6SOUA0"
         }
      ]
   },
   {
      "bea_order":[
      ]
   }
]

Expected Output:

(The value of flag is hardcoded)

[
   {
      "id":"a3I1T000003E6SQUA0",
      "flag":"false"
   },
   {
      "id":"a3Iq0000000OhnREAS",
      "flag":"false"
   },
   {
      "id":"a3Iq0000000OhnWEAS",
      "flag":"false"
   },
   {
      "id":"a3I1T000003E6SOUA0",
      "flag":"false"
   }
]

Mapping I tried:

%dw 2.0
output application/json
---
payload.bea_order filter ($.Id != null) map () -> {
    id : $.Id,
    flag : 'false'
}

Can you pl advice how to get the expected output.

Thanks

Yatan