                 <select id="testInvoiceId" class="form-control">
                            <option value="">Select an invoice (optional)</option>
                            <!-- This would be populated with actual invoices -->
                        </select>
                        <small class="form-text text-muted">
                            If selected, actual invoice data will be used for template variables
                        </small>
                    </div>
                </form>
     