找不到聊天消息的Steam UMQID

Using Golang, I am trying to send a chat message through Steam. The requirements for the post are

  • jsonp: jQuery1111021217753615295387_1460262983441 <- I am able to get this one

  • umqid: 6271781725479270872 <- I am unable to understand what this is and how to retreive it.

  • type: saytext <- I am able to get this one

  • steamid_dst: 76561198208696745 <- I am able to get this one
  • text: foobar <- I am able to get this one
  • access_token: 87e689c612b38f535a4d2b645b3aa3a7 <- I am able to get this one
  • _: 1460262983442 <- I am able to get this one

I understand all the variables required and am able to use them except for the UMQID variable. I have been through Steam's javascript source code over and over trying to figure out what the value of it is and how they generate the value but I haven't managed to understand it.

I've even been through someone else's Golang source code (line 211) which does exactly what I am aiming for but I still can't even figure out how they got the UMQID.

If anyone could explain how I am able to get the UMQID so I can post https://api.steampowered.com/ISteamWebUserPresenceOAuth/Message/v0001/ to send a Steam message, it would be greatly appreciated.