Correct. The documentation says you must buy either 3 postcards or 10 from within the app. 3 postcards sent internationally cost 168CZK = $7.64. 3 postcards

Correct. The documentation says you must buy either 3 postcards or 10 from within the app. 3 postcards sent internationally cost 168CZK = $7.64. 3 postcards sent to the EU cost €6.34.