How to embed value on Customer record in Sales Order - The field I placed only shows when screen calls back

@dgross Write a field updated event for the CUSTOMER ID in the Sales Order screen to fetch the COA field value from the Customers screen and assign it in the Sales Order screen custom COA field.

Here is the sample code for your reference.

 public class SOOrdeEntryExt : PXGraphExtension<SOOrderEntry>
    {

        protected virtual void SOOrder_CustomerID_FieldUpdated(PXCache cache, PXFieldUpdatedEventArgs e, PXFieldUpdated InvokeBaseHandler)
        {
            InvokeBaseHandler?.Invoke(cache, e);
            SOOrder row = e.Row as SOOrder;
            if (row != null)
            {
                Customer objCustomer = Customer.PK.Find(Base, row.CustomerID);
                SOOrderExt rowExt = row.GetExtension<SOOrderExt>();
                CustomerExt CustomerExt = objCustomer.GetExtension<CustomerExt>();
                if (objCustomer != null)
                {
                    rowExt.usrCOA = CustomerExt.usrCOA;
                }
            }
        }

    }