This is so frustrating and the reason I took so long to join discord. The useless random numbers at the end of usernames.
When someone irl asks me for my social media, I tell them everything except for discord. Why? Because I can't remember than random 4 digit code at the end. The exact same thing happens when I ask other people. It has happened at least twice, I asked for their username and they just give me their username, not the last 4 digits, since they didn't choose the numbers, and thus, don't remember (or even know its a thing).
No other social media does this, and it makes adding people extremely difficult. There isn't even a reason for it that I can think of.