Can't Prepare Invoice - Value cannot be null. Parameter name: value

I’m trying to prepare an invoice from a shipment, but I’m getting the following error.

Here is a screenshot from the trace

   at PX.Data.PXFirstChanceExceptionLogger.ProfilerFirstChanceException(Object o, FirstChanceExceptionEventArgs args)
   at System.Xml.Linq.XElement.set_Value(String value)
   at AmazonAcumatica.BZSOInvoiceEntryExt.InvoiceOrder(InvoiceOrderArgs args, InvoiceOrderDelegate baseMethod)
   at PX.Commerce.Objects.BCSOInvoiceEntryExt.InvoiceOrder(InvoiceOrderArgs args, InvoiceOrderDelegate handler)
   at PX.Objects.SO.SOOrderEntry.InvoiceOrder(Dictionary`2 parameters, IEnumerable`1 list, InvoiceList created, Boolean isMassProcess, ActionFlow quickProcessFlow, Boolean groupByCustomerOrderNumber)
   at PX.Objects.SO.SOOrderEntry.InvoiceOrders(List`1 list, Dictionary`2 arguments, Boolean massProcess, ActionFlow quickProcessFlow)
   at PX.Objects.SO.GraphExtensions.SOOrderEntryExt.Blanket.InvoiceOrders(List`1 list, Dictionary`2 arguments, Boolean massProcess, ActionFlow quickProcessFlow, Action`4 baseMethod)
   at Wrapper.PX.Objects.SO.Cst_SOOrderEntry.InvoiceOrdersGeneratedWrapper(SOOrderEntry g, List`1 , Dictionary`2 , Boolean , ActionFlow )
   at PX.Objects.SO.SOOrderEntry.<>c__DisplayClass135_0.<PrepareInvoice>b__0()
   at PX.Concurrency.CancellationIgnorantExtensions.RunWithCancellationViaThreadAbort(Action method, CancellationToken cancellationToken)
   at PX.Concurrency.CancellationIgnorantExtensions.<>c__DisplayClass1_0.<ToCancellationViaThreadAbort>b__0(CancellationToken cancellationToken)
   at PX.Concurrency.Internal.PXLongOperationPars.PopAndRunDelegate(CancellationToken cancellationToken)
   at PX.Concurrency.Internal.RuntimeLongOperationManager.PerformOperation(PXLongOperationPars p)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at PX.Concurrency.Internal.PXThreadPool.RunItem(RequestItem item)
   at PX.Concurrency.Internal.PXThreadPool.Run()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()