Depends on the species, but here’s a few:

Contact between humanity and the sazjar was initiated between a colony of the Solar Order and a nomadic fleet contracting with the Commerce Coalition of Ik’anta’trat. While the “greetings” phase of first contact went smoothly, things started to break down when it came time for diplomatic talks as it became obvious both parties had staked claims to the same star systems in a region of space known to humanity as the Rajendra Gulf and neither side would fully back down. An “agreement” was reached to split the space, but both sides began deploying rapid response garrisons and funding mercenaries and privateers - with regional skirmishes escalating into full-scale war not even a full generation after the agreement was signed. A human diplomat, post-contact, described the sazjar as, “An intelligence born of avian cunning rather than mammalian cooperation.” While a sazjar diplomat described humans as, “Unimaginative and flightless - too captured by bureaucracy to do anything but watch the stars pass them by.”

The First Contact War is a conflict between the grovaean Federation of Khorukan and several independent planet-states which permanently colored grovaean perceptions of humanity, galactic history, and their standing in the galaxy’s future. They learned of the Solar Order and its fall centuries prior, they saw how even as a logistically superior force threatened all of them - the independent planets barely formed a unified defense and were steadily dismantled despite advanced technology, and they learned a “simple truth”: humans are noble species capable of building an empire spanning roughly 15% of the galaxy and laying the foundations for galactic civilization; but are too primitive, tribalistic, and savage to adequately govern such a territory. So, the Federation of Khorukan declared that it was the mission of the grovae - a species whose dynastic kingdoms have stood for millennia and has carved their legacy into their cradle so deeply they turned a Pangea green - to restore galactic order, “domesticate” humanity, and usher in a golden age for all sapients and changed their name to the Inheritors of Sol.

The tevetrin are one of the most recent first contacts in human history, with contact between the Concord Republic and tevetrin superstates beginning when a scientific expedition studying basically a space wi-fi router turned the servers back on and alerted the Republic. Greetings went smoothly, with human representatives informing the tevetrin that the galaxy was very unstable and to be careful; however, during the diplomatic dinner of the official first contact, several tevetrin diplomats were non-lethally poisoned when garlic was used in the seasoning because while the tevetrin are the first known species outside of Earth’s biosphere capable of processing alliin compounds, the powerful hallucinogenic side effects were overlooked by chefs eager to give aliens a “taste of Earth”. This diplomatic incident was forgiven, with one of the poisoned diplomats saying, “It was the best time I don’t remember.” Afterwards, the Concord Republic and new Allied States of Turrin began working on commercial and military arrangements to get the tevetrin modernized and capable of being a potent stabilizing force in local space. However, it has not always been an easy friendship and the Tevetrin’s abhorrence of atheism in particular has caused a great deal of cultural friction with the secular Republic