Custom feature problem: Create Blanket Sales order button

I have created a shortcut button for Create Blanket Sales Order on the Sales Order Menu and on the Customers three dots menu.

This feature is used to: from creating a customer to creating a blanket sales order in a single click.

However, I have a problem: when I click the "Create Blanket Sales Order" button, it goes to the Sales Orders page then I notice that the "Create Child Orders" button is not displayed.

Also it works properly if I select the order type manually.
 

Please help me see if I am wrong or missing any part of the code. Thank you everyone for your help.

Here is the code
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namespace PX.Objects.AR
{
 
    [PXCacheName("SOOrder Extension")]
    public class SOOrderExt : PXCacheExtension<SOOrder>
    {
        #region UsrCreateChildOrders
        [PXBool]
        [PXUIField(DisplayName = "Create Child Orders")]
        public virtual bool? UsrCreateChildOrders { get; set; }
        public abstract class usrCreateChildOrders : PX.Data.BQL.BqlBool.Field<usrCreateChildOrders> { }
        #endregion
    }
  
          
     public class CustomerMaint_Extension : PXGraphExtension<CustomerMaint>
    {
        public PXAction<Customer> newBlanketSalesOrder;

        [PXUIField(DisplayName = "Create Blanket Sales Order")]
        [PXButton]
        public virtual IEnumerable NewBlanketSalesOrder(PXAdapter adapter)
        {
            Customer customer = Base.BAccount.Current;
            if (customer != null && customer.BAccountID > 0L)
            {
                SOOrderEntry soEntry = PXGraph.CreateInstance<SOOrderEntry>();
                soEntry.Clear();
                SOOrder newDoc = (SOOrder)soEntry.Document.Cache.Insert();
                newDoc.BranchID = null;
                soEntry.Document.Cache.SetValueExt<SOOrder.customerID>(newDoc, customer.BAccountID);
                soEntry.Document.Cache.SetValueExt<SOOrder.orderType>(newDoc, "BL"); // Set SOOrder Type here
                newDoc.ContactID = customer.PrimaryContactID < 0L ? null : customer.PrimaryContactID;
                soEntry.customer.Current.CreditRule = customer.CreditRule;
                if (soEntry.Document.Current.FreightTaxCategoryID != null)
                {
                    SOOrder createdOrder = (SOOrder)soEntry.Document.Cache.CreateCopy(soEntry.Document.Current);
                    soEntry.Document.Current.FreightTaxCategoryID = null;
                    soEntry.Document.Update(createdOrder);
                }

                // Update the order type configuration check
                var orderType = PXSelect<SOOrderType,
                    Where<SOOrderType.orderType, Equal<Required<SOOrderType.orderType>>>>.
                    Select(Base, "BL").FirstOrDefault();

                if (orderType != null && orderType.GetItem<SOOrderType>().Behavior != "BL")
                {
                    throw new PXException("The specified Order Type is not configured as a Blanket Order Type.");
                }

                throw new PXRedirectRequiredException(soEntry, "SO301000");
            }
            return adapter.Get();
        }
    }        
 }​​​​​​​