ls it correct to refer to Japan as "Nihon" or "Nippon"?

In 1934, the Ministry of Education's Provisional Deliberation Council on the Japanese Language designated Nippon as the official name.
Until this time, usage was random.
However, the use of Nippon was not decreed by the law, and even today, both names are commonly used.
Since postage stamps are marked Nippon and Japanese athletes sent overseas often wear uniforms emblazoned Nippon, it can be said that Nippon is regarded as the official name for Japan.