Generating deep nested JSON palyload out of Oracle SQL

I have a need to generate a three level nested JSON payload out of Oracle tables. I have described two approaches I have used to accomplish this and neither of them work. Please advise where am I going wrong!

Approach 1

Following select is supposed to generate a single json clob containing header, line and detail line tables. You will see that I am trying to get header, lines and distribution lines payload but its not working. I am getting header rows repeating with every line rows. So, as a result when this payload goes into a webservice, because header row is repeating, webservice will throw an error. How can I make header row not repeat with every line row?

select json_object
(
KEY 'InvoiceNumber'   VALUE  h.document_id,
KEY 'InvoiceCurrency' VALUE  'USD',
KEY 'InvoiceAmount'   VALUE  h.amount,
KEY 'InvoiceDate'     VALUE  h.trx_date,
KEY 'BusinessUnit'    VALUE  'ABCD Corp',
KEY 'Supplier'        VALUE  'NASA',
KEY 'SupplierSite'    VALUE  'PHYSICAL',
KEY 'InvoiceGroup'    VALUE  'MoonLander',
KEY 'Description'     VALUE  'Some Description',
KEY 'invoiceLines' VALUE  json_array
       (
        json_object 
           ( KEY 'LineNumber' VALUE t.line_id,
             KEY 'LineAmount' VALUE t.line_Value,
             KEY 'invoiceDistributions' VALUE json_array 
            (
              json_object 
              (
               KEY 'DistributionLineNumber' VALUE t.line_id,
               KEY 'DistributionLineType'   VALUE 'Item',
               KEY 'DistributionAmount'     VALUE  t.line_Value
              )
            )
            ))FORMAT JSON
    )JSON_VALUE
INTO aCLOB
from XXRR_HDR_STG h,
     XXRR_LINE_STG t
where t.document_id = h.document_id
and  h.document_id = 543210
order by t.line_id;

Approach 2

This approach uses Json Object and arrays. This is my preferable option but this gives Json Syntax error during runtime.

  FOR i IN gethdrrec LOOP
        -- Create JSON payload
            l_json.put('InvoiceNumber',i.document_id);
            l_json.put('InvoiceCurrency','USD');
            l_json.put('InvoiceAmount',i.amount);
            l_json.put('InvoiceDate', i.trx_date);
            l_json.put('BusinessUnit', 'ABCD Corp');
            l_json.put('Supplier', 'NASA');
            l_json.put('SupplierSite','PHYSICAL');
            l_json.put('InvoiceGroup','RR');
            l_json.put('Description', 'Some Descr');
            
            FOR j IN getlnrec(i.document_id) LOOP

              l_children.append(json_object_t('
             {  
                "LineNumber": "'|| j.line_id || '",
                "LineAmount": "'|| j.line_value|| '",
             }'));
              l_grandchild.append(json_object_t('
                { "DistributionLineNumber": "'|| j.line_id || '",
                  "DistributionLineType": "Item",
                  "DistributionAmount":"'|| j.line_value|| '",
                  "DistributionCombination": "254.000.000.2111010.000.0.0"
                 }'
                ));              
            END LOOP;
         
          END LOOP;

            l_json.put('invoiceLines', l_children);
            l_json.put('invoiceDistributions',l_grandchild);
            

        envelope := l_json.to_clob;

Finally here is the example payload structure I am trying to generate using above methods

{
    "InvoiceNumber": "MA_APInvoicex1",
    "InvoiceCurrency": "USD",
    "InvoiceAmount": 2212.75,
    "InvoiceDate": "2023-07-07",
    "BusinessUnit": "ABC Corp",
    "Supplier": "NASA",
    "SupplierSite": "Saint Paul",
    "InvoiceGroup": "July2023",
    "Description": "Office Supplies", 
    "invoiceLines": [{
        "LineNumber": 1,
        "LineAmount": 2112.75,
        "invoiceDistributions": [{
            "DistributionLineNumber": 1,
            "DistributionLineType": "Item",
            "DistributionAmount": 2112.75
        }]
        },
        {
            "LineNumber": 2,
            "LineType": "Freight",
            "LineAmount": 100,
            "ProrateAcrossAllItemsFlag": true,
            "invoiceDistributions": [{
                "DistributionLineNumber": 2,
                "DistributionLineType": "Item",
                "DistributionAmount": 2112.75
                 }]
        },{
            "LineNumber": 3,
            "LineType": "Freight",
            "LineAmount": 100,
            "ProrateAcrossAllItemsFlag": true,
            "invoiceDistributions": [{
                "DistributionLineNumber": 3,
                "DistributionLineType": "Item",
                "DistributionAmount": 2112.75
              }]
        }]
}

Here are tables to produce above query as requested by @MT0

CREATE TABLE xxrr_hdr_stg(document_id, amount, trx_date) AS
SELECT 543210, 100, SYSDATE FROM DUAL

CREATE TABLE xxrr_line_stg(document_id, line_id, line_value) AS
SELECT 543210, 1, 2112.75 FROM DUAL;

INSERT INTO  xxrr_line_stg(document_id, line_id, line_value) 
SELECT 543210, 2, 2112.75 FROM DUAL;

INSERT INTO  xxrr_line_stg(document_id, line_id, line_value) 
SELECT 543210, 3, 2112.75 FROM DUAL;

commit;

Please advise.

Thank you ,
Darsh