Once you arrive at Mountain Knot city you will discover that the woman in charge, Lockne, is very much against you and the UCA. She will not allow you to connect them to the Chiral network. Not sure why you can’t just stuff the keychain into the terminal and connect it whether she likes it or not.
Once she ends the call, you will be tasked with changing Locknes mind. The quest doesn’t give you any clues and as hard as you look to get some hidden meaning, there isn’t much. You need to convince her to change her mind. If you were paying attention during the conversation, you might be able to piece it together. If not, the game does tell you, just in a secret way.
You could waste a lot of time running to all the knot cities hoping someone will give you a clue, but the secret is actually hidden in your wrist. Press the options button and check your emails and you will see one that has a yellow title. Open this up and you will find out what you need to do.
This video will show you what you need to do to find the email in the games menu.