Hahah, but of course! Would you send someone a letter without knowing their address? Digital mail works in much the same way! Or magic mail, in this case.

[He opens his phone and gestures for Jae-ha to do the same, pointing out the right screen to him for finding his username, entering another person's (his is mephychan!), sending a message... how thoughtful!!]

[But no, all of this was a distraction so he could quietly snap a picture of Jae-ha on his own phone and send it to him in a message. u got mail.]