iMessage will not (re)connect on iMac

Do you have 2 step verification enabled on your Apple ID?

Apple ID - Two Step Verifications FAQ

Two-step authentication for iMessage and FaceTime

Hi,

It does seem that if Messages is open and stays open when you set up 2 Step Verification it can stay in this state until the app is Quit.

This means it could be quite some time before you get asked to set up a Specific Password.

If the iMac is not logged in to some services that it will not appear in the list.
So if the iMessages account is the only thing on that Mac that would be logged in with that ID then the Mac will not appear in the list (I.e. iTunes or Mail is not set up to use it as you use the iPad as the main device).

8:55 pm Tuesday; February 16, 2016

Hi,

When I checked the Apple ID site a little while ago and looked at the devices it did tell why some might appear in the list.

Check your Apple ID device list to see where you're signed in - Apple Support

It seems that some can be listed if they use a linked email in one app that is not used elsewhere.

For Instance I have my Original Apple ID which is based on a Dial-Up service I once had.

When iCloud came out I linked it to iCloud and got an @me.com email as well and later an @iCloud.com one as well.

For some things I can use them independently.

I tend to use the @me.com one for iCloud on the iPhone, Mac and iPad.

I use the original Apple ID in the iMessages Account on the same devices.

I could add another iPhone to the set up and use just the Original ID and not worry about linking it to iCloud.

This iPhone would then appear in the list of devices even though only one app was using the ID.

Whilst my set up of using different parts of the Apple ID/iCloud ID I could also see that you might have only set up Messages on your Mac.

I am trying to find out if my two older computers that don't have software to do iCloud will show up if I restart up iTunes.

I am stuck at the moment I as cannot remember one of the answers to one of my Security questions.

If you have had two Step Verification since 2014 has the Mac and it's version of Messages been logged in all that time ?
I don't use it myself but my understanding is that if an app is logged in at the time it is set up the Precess of needing an separate Password for that app does not happen until it needs to log in again.

I notice that there are not ways of deleting an ID either.

The way to add a device is to use an ID that is linked to the iCloud ID on a device and it should appear.

Currently as I said above I am trying to check in my MacBook Pro will get added now I have Logged in via iTunes

7:47 pm Wednesday; February 17, 2016

Hi,

I managed to get accepted back on the Apple ID site and I changed the Questions.

My MacBook Pro ver 1,1 has not been added since I restarted iTunes on it with the Apple ID password so it does seem the list can be incomplete for several reasons.

I would guess that there is an OS X factor in there somewhere.

I would try resetting the Applications Specific Password for Messages

8:44 pm Friday; February 19, 2016