Bank Deposit REST API. How to add payments?

If anyone finds themselves in the same boat,

I was able to get this working by adding a new child DAC mapped to a separate detail point in the webservice and then overriding the Persist method of CADepositEntry so that it if any records were added to this new DAC it then adds them into the Details cache using the Base.AddPaymentInfoBatch. Also cancels an attempt to persist to the PaymentInsert DAC.

 public delegate void PersistDelegate();
 [PXOverride]
 public void Persist(PersistDelegate baseMethod)
 {

     // Retrieve the current CADeposit record.
     CADeposit deposit = this.Base.Document.Current;
     if (deposit == null) return;

     // Prepare a list to store PaymentInfo records to be added.
     List<PaymentInfo> paymentsToAdd = new List<PaymentInfo>();

     // Iterate over each detail record in the UnboundPayments view.
     foreach (BCCAPaymentInsert detail in UnboundPayments.Select())
     {
         // Extract necessary fields from the detail record.
         string docModule = detail.OrigModule;
         string docType = detail.OrigDocType;
         string refNbr = detail.OrigRefNbr;

         // Ensure all fields are non-null before proceeding.
         if (docModule != null && docType != null && refNbr != null)
         {
             // Query the AvailablePayments view to find a matching payment.
             // Correct filters need to be applied to PaymentFilter
             var query = Base.AvailablePayments.Select().RowCast<PaymentInfo>().FirstOrDefault(pi =>
                             pi.DocType == docType &&
                             pi.RefNbr == refNbr &&
                             pi.Module == docModule);

             // If a matching payment is found, add it to the list.
             if (query != null)
             {
                 paymentsToAdd.Add(query);
             }
             else
             {
                 // Throw an exception if no matching payment is found.
                 string exceptionMessage = String.Format(BCCA.Messages.PaymentMissingFromAvailablePayments, refNbr);
                 throw new PXException(exceptionMessage);
             }
         }
     }

     // If there are payments to add, process them using the native method.
     if (paymentsToAdd.Count > 0)
     {
         Base.AddPaymentInfoBatch(paymentsToAdd);
     }

     // Clear the cache of UnboundPayments to remove processed records.
     UnboundPayments.Cache.Clear();

     // Call the base Persist method.
     baseMethod();
 }


 protected void _(Events.RowPersisting<BCCAPaymentInsert> e)
 {
     e.Cancel = true;
 }