Oracle 18c

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create or replace PROCEDURE ETA_JSON_SERIALIZE (json_in IN CLOB, can_str IN OUT VARCHAR2)
IS
    l_element   JSON_ELEMENT_T;
    l_child     JSON_ELEMENT_T;
    l_object    JSON_OBJECT_T;
    l_array     JSON_ARRAY_T;
    l_keys      JSON_KEY_LIST;
    l_str       VARCHAR2(32767);
    FUNCTION parseScalar(
      p_element IN JSON_ELEMENT_T
    ) RETURN VARCHAR2
    IS
    BEGIN
      RETURN CASE
             WHEN p_element.is_String()
             THEN 'String'
             WHEN p_element.is_Number()
             THEN 'Number'
             ELSE 'Other Scalar'
             END || CHR(10);
      
    END;
BEGIN
    l_element := JSON_ELEMENT_T.parse( json_in );
    l_element.on_Error(1);
    FOR i IN 0 .. l_element.get_Size - 1 LOOP
        IF l_element.is_Scalar() THEN
            l_str := l_str || parseScalar(l_element);
        ELSIF l_element.is_Object() THEN
            l_str := l_str || 'Object:' || CHR(10);
            l_object := JSON_OBJECT_T.parse( json_in );
            l_object.on_Error(1);
            l_keys := l_object.get_Keys();
            l_str := l_str || '     Element Size: ' || l_element.get_Size || CHR(10);
            l_str := l_str || '     Key Count: ' || l_keys.COUNT || CHR(10);
            FOR j IN l_keys.FIRST .. l_keys.LAST LOOP
              l_child := l_object.get( l_keys(j) );
              IF l_child.is_Scalar() THEN
                l_str := l_str || parseScalar(l_child);
              ELSE
                ETA_JSON_SERIALIZE( l_child.to_Clob(), l_str );
              END IF;
            END LOOP;
        ELSIF l_element.is_Array() THEN
            l_str := l_str || 'Array:' || CHR(10);
            l_array := JSON_ARRAY_T.parse( json_in );
            l_array.on_Error(1);
            l_str := l_str || '     Element Size: ' || l_element.get_Size || CHR(10);
            l_str := l_str || '     Array Size: ' || l_array.get_Size || CHR(10);
            FOR j IN 0 .. l_array.get_Size - 1 LOOP
                l_child := l_array.get(j);
                IF l_child.is_Scalar() THEN
                  l_str := l_str || parseScalar(l_child);
                ELSE
                  ETA_JSON_SERIALIZE( l_child.to_Clob(), l_str );
                END IF;
            END LOOP;
        ELSE
            l_str := l_str || 'Other Type' || CHR(10);
        END IF;
    END LOOP;
    can_str := l_str;
END;
/
SELECT * FROM USER_ERRORS;
DECLARE
   can_str  VARCHAR2(32767);
   l_doc    CLOB :=
   '{
   "documents": [{
      "issuer": {
         "type": "B",
         "id": "301188475",
         "name": "Hakim Misr Paco (POS-0)",
         "address": {
            "branchID": "-1",
            "country": "EG",
            "governate": "Cairo",
            "regionCity": "Nasr City",
            "street": "Mostafa El Nahas",
            "buildingNumber": "65"
         }
      },
      "receiver": {
         "type": "P",
         "id": " 29409200104255",
         "name": "Karim Ahmed Abdelhakim Hashem",
         "address": {
            "country": "EG",
            "governate": "Cairo",
            "regionCity": "Nasr City",
            "street": "Mostafa El Nahas",
            "buildingNumber": "65"
         }
      },
      "documentType": "I",
      "documentTypeVersion": "0.9",
      "dateTimeIssued": "2022-11-19T23:59:59Z",
      "taxpayerActivityCode": "2220",
      "internalID": "0-1",
      "invoiceLines": [{
         "description": "KFC_Test",
         "itemType": "GS1",
         "itemCode": "10006331",
         "unitType": "EA",
         "quantity": 1000,
         "unitValue": {
            "currencySold": "EGP",
            "amountEGP": 0.10000,
            "amountSold": 0
         },
         "salesTotal": 100,
         "total": 114,
         "valueDifference": 0,
         "totalTaxableFees": 0,
         "netTotal": 100,
         "itemsDiscount": 0,
         "discount": {
            "rate": 0,
            "amount": 0
         },
         "taxableItems": [{
            "taxType": "T1",
            "amount": 14,
            "subType": "V009",
            "rate": 14
         }],
         "internalCode": "Test_110"
      }],
      "totalSalesAmount": 100,
      "totalDiscountAmount": 0,
      "netAmount": 100,
      "taxTotals": [{
         "taxType": "T1",
         "amount": 14
      }],
      "extraDiscountAmount": 0,
      "totalItemsDiscountAmount": 0,
      "totalAmount": 114,
      "signatures": [{
         "signatureType": "I",
         "value": "NA"
      }]
   }]
}';
BEGIN 
  DBMS_OUTPUT.ENABLE();
  ETA_JSON_SERIALIZE(l_doc, can_str);
  DBMS_OUTPUT.PUT_LINE(can_str);
END;
/
1 rows affected

dbms_output:
Object:
     Element Size: 2
     Key Count: 2
String
String
Object:
     Element Size: 2
     Key Count: 2
String
String