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Germany: Employee and Entrepreneur at same time (for getting AppStore payments)
(Selling apps is AFAIK business, not freelancing - unless the type of app you produce is considered a freelancing subject. The tax office will give you a questionnaire and then decide).  As Einzelunternehmer, you can receive the payments for the apps to the same account where your wages go. However, there are lots of online accounts that do not cost fees, so consider to receive them on a separate account so you have the business and private kind of separate (for small Einzelunternehmer, there is no legal separation between business and private money - you have full liability with your private money for the business).  The local chamber of commerce can tell you everything about setting up such a business, ask them (you'll probably have to become a member there anyways). They have information as well on VAT (Umsatzsteuer, USt) which you need to declare unless you get an exemption (probably possible), and about Gewerbesteuer (the income tax of the business) etc. For the tax, you have "subforms"  for the income tax e.g. for wages and for business income, so you just submit both with the main form. You'll get an appropriate tax number when registering the business.  Social security/insurance: as long as the app selling is only a side business, the social insurance payments for your main job completely cover the side job as well. You need to make sure that your employment contract is compatible with the app business, though.  A quick search indicates that there is a tax treaty between Germany and the Ukraine, Wikipedia says there are no contracts about social insurance in effect (yet).