Depending on what it's for you can add it as a link in:

/templates/template_name/includes/menu.tpl for the main menu or the following for the top right toolbar:

/templates/template_name/includes/toolbar.tpl

<li><a href="{$WEB_ROOT}/index.php?m=clientverification">Add/View Verificaton Data</a></li>

Since WHMCS Services now has several active versions and also different types of updates, there are 4 types of updates. These are:

Major Release: A major release is a new main version and contains changes to the core and usually introduces new features. 1.0 and 2.0 are major releases. You can recognize one such an update also the first number of the version number changes. With Major Releases there is always only one complete upgrade and no incremental.

Minor Release: A Minor release includes new features and can also include changes to the schema and prepare major updates. The versions 2.1.0, 2.2.0 and 2.3.0 are for example Minor Releases. These updates always change the average number. With Minor Releases there is always only one complete upgrade and no incremental.

Maintenance Release: Maintenance Release is, as the name suggests, maintenance updates where bugs are fixed. The versions 1.3.1 and 1.1.2 are, for example, such updates. Here the last number always changes. There is also a small incremental update for maintenance releases.

Security Release: Security releases contain security-relevant updates which, for example, close security gaps. These updates are usually accompanied by maintenance releases and should be implemented promptly. Here again, the last number of the version number changes.

Depending on what it's for you can add it as a link in:

/templates/template_name/includes/menu.tpl for the main menu or the following for the top right toolbar:

/templates/template_name/includes/toolbar.tpl

<li><a href="{$WEB_ROOT}/index.php?m=loginverifypin">Login verify</a></li>

Hexa Extra Template 
You can edit header.tpl file (header.tpl.new can be renamed to header.tpl in overrides folder). Overrides folder will help with keeping customization during updates.
The navbar li item can be duplicated and customized for your needs.

<a href="/index.php?m=loginverifypin">Login verify</a>

Version 4.5.x you don't need to edit any template you can do of the Hexa Extra Menu

Flattern Extra Template

You can edit header.tpl file (header.tpl.new can be renamed to header.tpl in overrides folder). Overrides folder will help with keeping customization during updates.
The navbar li item can be 

<li><a href="index.php?m=clientnotifyn">Notification Settings</a></li>

Depending on what it's for you can add it as a link in:

/templates/template_name/includes/menu.tpl for the main menu or the following for the top right toolbar:

/templates/template_name/includes/toolbar.tpl

<li><a href="{$WEB_ROOT}/index.php?m=clientnotify">Notification Settings</a></li>

Version: 2.1.4 Released (12/01/2021)
Maintenance

Fixed Problem with WHMCS v8 gateways
Updated About Page
Updated Remove Support for PHP 5.6 to 7.0

Version: 2.1.3 Released (04/02/2018)
Maintenance

Update to work with WHMCS 7.5
Update to work with PHP 7.2 and Ioncube 10.1

Version: 2.1.2 Released (14/10/2017)
Maintenance

Updated Improve License Check
Updated WHMCS v7.3 support
Updated Make working with PHP 7 and Capsule
Updated WHMCSSERIVCES help page added

Version: 2.1.1 Released (10/10/2016)
Maintenance

Updated WHMCS v7 support

Version: 2.1.0 Released (25/10/2015)
Maintenance

Updated License Code

Version: 6.2.1 Released (01/03/2024)
Maintenance

Fixed support for ionCube Loader v13
Updated Licence System with Cloudflare
Updated Improve ionCube Loader

Version: 6.2.0 Released (11/28/2023)
Minor

Added A note on the Services page
Added Top bar to the top of the page
Added Support PHP 8.2
Fixed PHP 8.1
Updated Remove Support for WHMCS V8.4.x to 8.5.x

Version: 6.1.1 Released (12/04/2022)
Maintenance

Added Italian Language
Fixed issue with display popup in special pages
Fixed support for ionCube Loader v12 and PHP 8.1
Updated Remove Support for PHP 7.1 to 7.3
Updated Remove Support for WHMCS V8.1.x to 8.3.x

Version: 6.1.0 Released (12/29/2021)
Minor

Added Add fund page banner
Updated New WHMCSServices menu to work with WHMCS 8. x
Fixed Problem with PHP 7. x
Fixed Problem with popup predefined styles
Fixed Button Not Functioning

Version: 6.0.0 Released (09/22/2020)
Stable

Added Admin User with many updates and improvements
Added New predefined popup list
Added New template notification
Added Archive notification feature
Added Start at notification
Added Preview popup
Added index.php to all directories
Fixed Admin issues
Fixed htaccess rewrite URL
Fixed breaking the third-party WHMCS theme called Control (impressivethemes)
Updated Module tables renewed
Updated Remove v4 Admin theme from distribution
Updated Remove Support for PHP 5.6 to 7.0

Version: 5.0.7 Released (12/03/2018)
Maintenance

Fixed blank HTML paragraph

Version: 5.0.6 Released (08/03/2018)
Maintenance

Fixed third-party WHMCS theme called  SwiftModders Themes
Fixed Expiry Date

Version: 5.0.5 Released (07/26/2018)
Maintenance

Fixed Correct language in about page
Fixed Product group notification
Updated New WHMCSServices menu to work with WHMCS 7.6
Updated Show alert when template missing

Version: 5.0.4 Released (06/04/2018)
Maintenance

Fixed PHP 7.1 and PHP 7.2
Fixed to work with WHMCS 7.5

Version: 5.0.3 Released (06/11/2017)
Maintenance

Fixed an improvement running in WHMCS 7.4
Fixed links added to the top notification

Version: 5.0.2 Released (15/10/2017)
Maintenance

Fixed Default WHMCS hook conflict problem
Updated WHMCS SERVICES help page added

Version: 5.0.1 Released (13/10/2017)
Maintenance

Fixed Upgrade from the 4.0 version problem
Fixed None multi-language problem

Version: 5.0.0 Released (10/10/2017)
Stable

Added Top notification
Added Popup notification
Added Allowing the client to show notifications with shortcodes
Added Set of custom colors and font added
Added Multi-languages
Added Custom CSS
Added Show notification to a product clients
Added Show notification to an Addon clients
Added Auto adding codes to the template file
Fixed Product Group

Version: 4.1.0 Released (30/01/2017)
Updated

Updated Improve the license call

Version: 4.0.0 Released (22/12/2016)
Stable

Fixed Middle notification does not show
Updated CKEditor Update
Updated New and faster licensing system implemented
Updated V7 Comparability
Updated Duplicate Button
Added Full recode of module helping the performance

Version: 3.1.0 Released (22/10/2015)
Maintenance

Updated License Code

Global settings:

 

Fixed small bug on WS Affiliates Plus 1.0.2 for WHMCS Now Available - https://www.whmcsservices.com/affiliatesplus.php

Changelog
1.0.2

Fixed Send email problem when order not accepted problem resolved

If you are looking for someone to develop a Custom WHMCS, Blesta, WISECP Application for you, whether it's for you to sell to other people; for your company to use; or whatever the reason, feel free to contact us for a quote. We will discuss the project with you and come up with a very reasonable and cost-effective price.

Our programming is primarily designed with the view to offer quality web solutions at affordable rates. Small enterprises can greatly benefit by getting affordable web solutions of high standards.

For more information, you can go to https://www.whmcsservices.com/customworks.php.

Chat with us through live support or send in a ticket if you would like more information.

Thanks, and we at WHMCS Services look forward to being the provider of your company's peace of mind...and your Programmer solution!

If you have any questions about our services, please chat with us at http://www.whmcsservices.com