Hello,
We can develop a web-based invoice system.
We have great skills with core Pho and Php-frameworks, HTML5, CSS3, Bootstrap, MySQL, CMS Wordpress, Opencart, Prestashop, Drupal, Joomla, Magento. You can see our profile here https://www.freelancer.com/u/Webln .
Let's discuss everything on chat!
With regards,
WebIn team.