Minimal Values of the JSON

Sample code for reference with mandatory attributes for each JSON:

Add Items JSON

{
 "addProducts": [
   {
     "fieldApiName": "Description_1__c",
     "objectApiName": "Product2",
     "isColumn": true,
     "isFilter": true
   },
   {
     "fieldApiName": "Unit_Type__c",
     "objectApiName": "Unit_of_Measure__c"
   },
   {
     "fieldApiName": "Type"
   }
 ]
}

Free Items JSON

{
 "freeItems": [
   {
     "fieldApiName": "Product__r.Description_1__c",
     "objectApiName": "Order_Item__c"
   },
   {
     "fieldApiName": "Quantity__c",
     "objectApiName": "Order_Item__c"
   }
 ]
}

Order Items JSON

{
  "orderItems": {
    "columnsConfiguration": [
      {
        "fieldApiName": "Product__r.Description_1__c",
        "objectApiName": "Order_Item__c",
        "visible": true
      },
      {
        "fieldApiName": "UoM__c",
        "objectApiName": "Order_Item__c"
      },
      {
        "editable": true,
        "fieldApiName": "Quantity__c",
        "fieldType": "number",
        "objectApiName": "Order_Item__c",
        "visible": true
      }
    ],
    "fixedColumns": 2,
    "maxNumberDeletes": 1000,
    "maxNumberUpdates": 1000
  }
}

Order Details JSON

{
 "orderdetails": [
   {
     "fieldApiName": "Name",
     "objectApiName": "Order__c"
   }
 ]
}

Order Page Header JSON

{
 "orderpageheader": [
   {
     "fieldApiName": "Order_Account__c",
     "objectApiName": "Order__c"
   }
 ]
}