The real point of this topic, was not very clearly explained from the beginning so let me clear this:
The Certificate of Residence is needed by a Buyer(in this case from Poland) from the Vendor(in this case Envato) in order to show to the Local Taxation Office(this case from Poland) that the Vendor pays its taxes in the country of residence(this case Australia).
This certificate is issued by the Vendor’s Taxation Office in accordance with the Commercial agreements between the 2 countries(this case Poland and Australia).
Not having this Certificate(in Poland), will legally compel the Buyer to pay an additional tax as though the object(licence) was produced in the Buyers country.
Hope I’ve succeeded to explain in human words.