Question: When did the city where the Yongle emperor greeted the person to whom the edict was addressed become the Chinese national capital?

Passages:
The Information Office of the State Council of the PRC preserves an edict of the Zhengtong Emperor (r. 1435–1449) addressed to the Karmapa in 1445, written after the latter's agent had brought holy relics to the Ming court. Zhengtong had the following message delivered to the Great Treasure Prince of Dharma, the Karmapa: During his travels beginning in 1403, Deshin Shekpa was induced by further exhortations by the Ming court to visit Nanjing by April 10, 1407. Norbu writes that the Yongle Emperor, following the tradition of Mongol emperors and their reverence for the Sakya lamas, showed an enormous amount of deference towards Deshin Shekpa. The Yongle Emperor came out of the palace in Nanjing to greet the Karmapa and did not require him to kowtow like a tributary vassal. According to Karma Thinley, the emperor gave the Karmapa the place of honor at his left, and on a higher throne than his own. Rossabi and others describe a similar arrangement made by Kublai Khan and the Sakya Phagpa lama, writing that Kublai would "sit on a lower platform than the Tibetan cleric" when receiving religious instructions from him. Nanjing ( listen; Chinese: 南京, "Southern Capital") is the city situated in the heartland of lower Yangtze River region in China, which has long been a major centre of culture, education, research, politics, economy, transport networks and tourism. It is the capital city of Jiangsu province of People's Republic of China and the second largest city in East China, with a total population of 8,216,100, and legally the capital of Republic of China which lost the mainland during the civil war. The city whose name means "Southern Capital" has a prominent place in Chinese history and culture, having served as the capitals of various Chinese dynasties, kingdoms and republican governments dating from the 3rd century AD to 1949. Prior to the advent of pinyin romanization, Nanjing's city name was spelled as Nanking or Nankin. Nanjing has a number of other names, and some historical names are now used as names of districts of the city, and among them there is the name Jiangning (江寧), whose former character Jiang (江, River) is the former part of the name Jiangsu and latter character Ning (寧, simplified form 宁, Peace) is the short name of Nanjing. When being the capital of a state, for instance, ROC, Jing (京) is adopted as the abbreviation of Nanjing. Although as a city located in southern part of China becoming Chinese national capital as early as in Jin dynasty, the name Nanjing was designated to the city in Ming dynasty, about a thousand years later. Nanjing is particularly known as Jinling (金陵, literally meaning Gold Mountain) and the old name has been used since the Warring States Period in Zhou Dynasty.

Supporting sentences:
During his travels beginning in 1403, Deshin Shekpa was induced by further exhortations by the Ming court to visit Nanjing by April 10, 1407. Although as a city located in southern part of China becoming Chinese national capital as early as in Jin dynasty, the name Nanjing was designated to the city in Ming dynasty, about a thousand years later.