The problem is there are a lot of detail that is different just for the sake of being different and those will suck your soul. There are interesting problems in billing. However most of the issues are another government has a law that is essentially the same as every other government, but some small detail is trivially different so you need to figure out which subset of customers that government covers and then apply those details correctly to them. Nothing hard about this, just the same old tax but the details are annoyingly different.

Note that you need to get the above details 100% correct in all cases. They can put you in prison for mistakes (almost always they will just fine the company a lot of money, but they have the right to apply prison and you never know when they will want to make an example of someone)