Why "LAST_INSERT_ID()" doesn't return anything here in a MySQL reader?

Question

I am trying to understand why the second LAST_INSERT_ID() command doesn't return anything in the reader after executing addInvoiceCommand. The reader keeps returning 0 rows. The first reader after addClientCommand works fine.

    using (var connection = new MySqlConnection(builder.ConnectionString))
            {
                await connection.OpenAsync();


                var addClientCommand = connection.CreateCommand();
                addClientCommand.CommandText = @"INSERT INTO client(clientName)
                VALUES(@ClientName);"; 

                
                addClientCommand.Parameters.AddWithValue("@ClientName", input.Client.ClientName);
                addClientCommand.ExecuteNonQueryAsync();

                var selectLastIdCommand = connection.CreateCommand();
                string lastInsertedId = "";
                selectLastIdCommand.CommandText = @"SELECT LAST_INSERT_ID();";

                using var reader = await selectLastIdCommand.ExecuteReaderAsync();
                while (reader.Read())
                {
                   lastInsertedId = reader[0].ToString();
                }

                reader.Close();


                
                var addInvoiceCommand = connection.CreateCommand();
                addInvoiceCommand.CommandText = @"INSERT INTO invoice(client_id,
                description, paymentTerms, invoiceDate, paymentDueDate,BillFromAddress,
                BillFromCity, BillFromCountry, BillFromPostal)
                VALUES(@client_id, @Description, @PaymentTerms, @InvoiceDate, @PaymentDueDate,
                @BillFromAddress, @BillFromCity,  @BillFromCountry, @BillFromPostal);";

                addInvoiceCommand.Parameters.AddWithValue("@client_id", Int32.Parse(lastInsertedId));
                addInvoiceCommand.Parameters.AddWithValue("@description", input.Description);
                addInvoiceCommand.Parameters.AddWithValue("@paymentTerms", input.PaymentTerms);
                addInvoiceCommand.Parameters.AddWithValue("@invoiceDate", input.InvoiceDate);
                addInvoiceCommand.Parameters.AddWithValue("@paymentDueDate", input.PaymentDue);
                addInvoiceCommand.Parameters.AddWithValue("@BillFromAddress", input.BillFromAddress);
                addInvoiceCommand.Parameters.AddWithValue("@BillFromCity", input.BillFromCity);
                addInvoiceCommand.Parameters.AddWithValue("@BillFromCountry", input.BillFromCountry);
                addInvoiceCommand.Parameters.AddWithValue("@BillFromPostal", input.BillFromPostal);
                addInvoiceCommand.ExecuteNonQueryAsync();
               

                var lastInvoiceIdCommand = connection.CreateCommand();
                string lastInvoiceId = "";
                lastInvoiceIdCommand.CommandText = @"SELECT LAST_INSERT_ID();";

                using var readerLastInvoiceId = await lastInvoiceIdCommand.ExecuteReaderAsync();
                while (readerLastInvoiceId.Read())
                {
                    lastInvoiceId = reader[0].ToString();
                }

                readerLastInvoiceId.Close();