In this academy he had an unsuccessful presentation in 1753 for the annual art competition, with the submission Fauno del cabrito (Kid Faun), and therefore got no pension to travel to Rome in 1758 (the scholarship was won by José del Castillo).
At twenty-two, however, he made his most clearly documented and best efforts, the fresco decoration of the ceiling and walls of the sacristy of the Virgin in the Basilica of Our Lady of the Pillar.
Inza primarily painted portraits, many of them confused with those of his countryman Francisco Goya due to their similar styles, making attributions tricky.
In the 1770s, he painted at least three portraits of Charles III of Spain, which are preserved in the Sociedad Económica de los Amigos del País in Zaragoza and the Royal Academy of Jurisprudence and Legislation, all signed.
He also painted a portrait of the poet Tomás de Iriarte y Oropesa in 1785, one of Manuel Godoy, Prince of the Peace (1773), and of the Dowager Countess of Benavente, Zamora (1782).