In 1415 Netter was sent by the king to the Council of Constance, where the English nation, though small in numbers, asserted its influence. He must have interrupted his residence at Constance by one, if not several, visits to his province. At the conclusion of the council he, with William Clynt, doctor in Divinity, and two knights, was sent by the English king on an embassy to the King of Poland, the Grand Duke of Lithuania, and the Grand master of the Teutonic Knights. The pope was represented by two Italian bishops, and the emperor by the Archbishop of Milan. The object of the mission was to bring about a mutual understanding and prevent the failure of the papal army against the Hussites. It has been asserted that on this occasion Netter converted Vytautas, Grand Duke of Lithuania, to Christianity, and was instrumental in his recognition as king and his subsequent coronation. Although all this is doubtful, it is possible that Netter did exercise some influence during his brief stay in eastern Europe, for he has been styled the Apostle of Lithuania; he also established several convents of his order in Prussia.