CAN'T SEND FRIEND REQUEST ON DISCORD

Hi , I know a person from 3yrs ago , we used to talk on discord and apparently both of us lost our discord main , we were friends on Roblox so they somehow texted me their new discord username, but since we could talk more Roblox I accidentally blocked on Roblox and then unblocked by now chat is gone and they aren't seeing to accept my request on Roblox, so coming to discord I have username but when I sent request it says they will have to friend you because they don't accept friend request, now I don't have any other ways to reach them out any help would great , I have discord username, Roblox account ( not friends there) and a yt channel, how can I reach them out