If you want to pay the income tax in Poland, you have to move to Poland (or spend in Poland more than 6 months in the year). It doesn't matter, who your client is, it only matters where you live (the proof being apartment contract, mobile plan, any bills, credit card transactions, neighbours etc).
If you want to pay the income tax in Poland, you have to move to Poland (or spend in Poland more than 6 months in the year). It doesn't matter, who your client is, it only matters where you live (the proof being apartment contract, mobile plan, any bills, credit card transactions, neighbours etc).