Writing Lunar Date in Khmer is for all official documents using in Cambodia's government if you have noticed.
And of course, it is also a hardest one for other people who are not in government office as we are mostly not using Lunar calendar in private but when we need to use it, we always check Lunar calendar issued by corresponding organization.
Here is a help tool: https://tools.wikischool.asia/KhmerLunar
The tool helps for writing the correct date and in Khmer language.
If you find this useful and also want to continue engage with WikiSchool, reach them at facebook.