I’m definitely not an expert in this area but the important thing to find out is the tax laws in both your country of residence and the other country you are advertising/reaching out to. Every country is different so you won’t get much useful specific advice here, but largely, the laws relate to where income is generated which determines if/how much tax you have to pay. Tax auditing systems have become more sophisticated in recent years so trails have become tighter back to where your income is received.