What is the etiquette of three kneels and nine knocks in the Ming Dynasty, and what ceremony was it used for?

Kneel down three times and knock nine heads. This is the most respectful way to salute.

At the beginning of the Ming dynasty, it was four or five times.

It was not until the Qing Dynasty came to power that the system of three kneeling and nine knocking was formed.

After Dingding in the Central Plains in the Qing Dynasty, the ritual of three kneels and nine knocks to worship heaven replaced the ritual of five worships and three knocks in the Ming Dynasty. In addition to the three-kneeling and nine-knocking ceremony for the emperor, Manchu customs should also respect this ceremony in the presence of the tributary state. However, due to the different customs and habits of different countries, when there was a protest against this gift, the Qing Dynasty pretended to be a heavenly country and easily condescended to give up this gift, consciously losing the face of a big country. Therefore, there are sometimes "etiquette disputes".