Adding Custom Field to Client Page

Hi,

I’ld like to format my client screen as in the screenshot below.

But I don’t seem to be able to save the data entered. Could anyone pls help confirm if my variables have been entered correctly?

                    <legend><?php echo trans('contact_information'); ?></legend>

                   <div class="form-group">
                        <label><?php echo trans('Contact Person'); ?>: </label>

                        <div class="controls">
                            <input type="text" name="client_custom_contact_person" id="client_custom_contact_person" class="form-control"
                                   value="<?php echo htmlspecialchars($this->mdl_clients->form_value('client_custom_contact_person')); ?>">
                        </div>
                    </div> 
<?php if ($invoice->client_custom_client_position) { ?>
<span><?php echo $invoice->client_custom_client_position; ?></span><br>
<?php } ?>

Thanks in advance.

Regards,
Michele

Can some body help with this idea? Im having the same kind of issue.