Updating Unit Price on a Sales Order in Completed State

Hello,

I am trying to build a customization where I want to make the Unit Price (CuryUnitPrice) column on SOLine editable even when the Sales Order is in the Completed state.

I have been able to make the field editable, and after updating the value, the Save button is also available to save the updated changes.
 

However, when I click the Save button and try to save the updated value, I am getting the following error:
 

Here is my code for the Graph Extension as well as the Workflow Extension.

Workflow Extension:

public class SOOrderEntry_Workflow_Ext : PXGraphExtension<PX.Objects.SO.SOOrderEntry_Workflow, SOOrderEntry>
{
    public static bool IsActive() => true;

    public override void Configure(PXScreenConfiguration config) =>
        Configure(config.GetScreenConfigurationContext<SOOrderEntry, SOOrder>());

    protected virtual void Configure(WorkflowContext<SOOrderEntry, SOOrder> context)
    {
        context.UpdateScreenConfigurationFor(screen =>
            screen.WithFlows(flows =>
                flows.Update<SOBehavior.sO>(flow =>
                    flow.WithFlowStates(states =>
                        states.Update<SOOrderStatus.completed>(state =>
                            state
                            .WithActions(acts =>
                            {
                                acts.Add(g => g.Save);
                                acts.Add(g => g.Cancel);
                            })
                            .WithFieldStates(fields =>
                            {
                                fields.RemoveField<SOLine.curyUnitPrice>();
                                fields.AddField<SOLine.curyUnitPrice>();
                            })
                        )
                    )
                )
            )
        );
    }
}

Graph Extension:

protected virtual void _(Events.RowSelected<SOLine> e, PXRowSelected baseHandler)
{
    baseHandler?.Invoke(e.Cache, e.Args);
    var line = e.Row;
    if (line == null) return;

    var order = Base.Document.Current;

    bool allowInCompleted = CanEdit(order, line);
    if (!allowInCompleted)
        return;

    Base.Document.Cache.AllowUpdate = true;
    Base.Transactions.Cache.AllowUpdate = true;

    PXUIFieldAttribute.SetEnabled<SOLine.curyUnitPrice>(e.Cache, line, true);

    if (line.ManualPrice != true)
        e.Cache.SetValueExt<SOLine.manualPrice>(line, true);
}

protected virtual void _(Events.RowSelected<SOOrder> e, PXRowSelected baseHandler)
{
    baseHandler?.Invoke(e.Cache, e.Args);
    var doc = e.Row;
    if (doc == null) return;

    bool completed = string.Equals(doc.Status, SOOrderStatus.Completed, StringComparison.OrdinalIgnoreCase);
    if (!completed) return;

    Base.Document.Cache.AllowUpdate = true;
    Base.Transactions.Cache.AllowUpdate = true;

    Base.Actions[nameof(SOOrderEntry.Save)]?.SetEnabled(true);
    Base.Actions[nameof(SOOrderEntry.Cancel)]?.SetEnabled(true);
}

If anyone could help me with this, it would be really helpful.

Kind Regards,
Dhruv