Left on request

A much more humiliating and frustrating experience than Left on Read

In the case of Left on Request the person you're messaging isn't even aware of your existence

It sometimes can be unintentional if the person you're trying to message is bombarded by DMs all day long she or he might miss you in the list of people trying to slide into their DMs

Jack: Zoey tells me to send her a DM but she's not responding to me, I don't even get a seen notification
Mike: guess you're left on request bro... She's popular and you're not the only guy looking for her