If you are abroad, you need to clearly understand what sources of income you have, as well as collect the necessary amount of evidence of the presence of a center of economic interests in Ukraine (evidence that will confirm the economic connection with the country). An example of this can be certificates on the availability of accounts in Ukrainian banks, real estate, the presence of a registered FOP, receipts for the payment of utility bills, certificates on the child's attendance at educational institutions, etc.
Carefully read the double taxation receipts, which clearly state what taxes you have to pay and where. If necessary, you can contact a tax consultant who will explain the correct algorithm of actions.
Please note that if you live abroad at your own expense or at the expense of social and pension benefits, such income is not taxable.