Custom WordPress Plugin & Theme
There are tons of WordPress plugins and themes available on the market, whether it's free or paid. But many people often need a unique one, a shape of their own ideas that will make their job done and ofcourse without adding new problems.
I have years experience of build custom WordPress plugins and themes, some of them are just add-ons or child themes to extend their parents functionality, some other are stand alone plugins and themes with unique solutions.
WordPress REST API
As a WordPress's built-in function to communicate with outside, WordPress REST API become a popular solution to bussiness models that require a reliable function to communicate between 2 or more WordPress sites like data synchronization, or even between WordPress with different systems like Mobile or Desktop apps.
I have been using WordPress REST API to some projects like WooCommerce stock sync, user frontend dashboard, and mobile app's online application data.
Plugin & Theme Enhancement
Not everyone happy with their installed plugins or themes, some of them are have a particular plugin installed on their site because it's the only plugin that cover most of their needs, but not all of them.
In this case, we need to create a custom plugin or child-theme to cover the stock plugin's lack, and on my experience, the enhancement can be on WordPress filters code, MySQL query, or even on front-end jQuery code.
WordPress Bug Fixing
Error happens, even on most used CMS like WordPress. With my experience, we can track down the error source without make the website down (off-line) so you won't loose any visitors, and then we can focus on create a custom plugin or modify the child-theme's code to patch the bugs.