It was a bit nerve racking as when i applied it was same day approval and Taipei is among the strictest embassies for approval. They are very much about evidence of income, business registration, Taipei was among the most popular embassies at the time, so I used a lot of posts to help my application, If they by chance request tax info then you just explain why you can not provide them, there are many genuine reasons why tax docs cannot be submitted so it is not mandatory
You don't have to provide tax info to get approved. I offered my tax docs when I applied (Taipei) in person, but they refused to take them as they don't use them for approval. Many other freelancers in various embassies also approved without submitting tax info
Some embassies Inc London ask for actual booking confirmation. London does not ask everyone though. Jakarta has tightened up its approval recently..more applicants now asked for interviews.