欸 is old Chinese and it is replaced and now more commonly written as the character 唉. It’s colloquially used in many places in different domains - be it dialogues of old Chinese drama or chinese games or even characters in it. Fun fact: Chinese language has more than 70,000 characters out of which only 20,000-30,000 is taught and used in everyday Chinese (Spoken and written) language. AFAIK, these are just exclamation sounds and do not necessarily have any meanings. Some other examples are 嗯, 哇 and so on.
