The coat of arms is the coat of arms of Prussia. This is a copper coin issued in the name of South Prussia, something like this example:
https://en.numista.com/26929 The date should be just to the left of the crown.
"South Prussia" was the name given by the Prussians to the territory they annexed from Poland after the Second and Third Partitions of Poland in 1793 and 1797. Due to the multi-ethnic (mostly Polish) nature of the territory in question, the coin's language is Latin rather than the usual German found on mainstream Prussian coins. The denomination is called a "grossus" in Latin, "groschen" in German and "grosz" in Polish. The territory became "independent" under French protection as the Duchy of Warsaw in 1807 after Prussia lost to Napoleonic France. After the Congress of Vienna in 1815, the territory was divided between Prussia and Russia; the Prussian piece did indeed become the Grand Duchy of Posen, but Posen did not issue its own coinage after 1815.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis