Screen sharing using Apple's Messages.app: troubleshooting

[SpeedThree]

If I am posting this in the wrong forum, would someone kindly point me toward the correct one?
I have a 2015 iMac, FusionHD, macOS 12.1.2.
I am trying to help seniors dealing with problems with their Macs.
90% of the time I am able to use Messages.app to view and control their Macs.
10% of the time I will extend the invitation to share screens, they will never receive it, and the attempt times out with something like: John Doe is not available for screen sharing.
I will carefully walk these folks through the process of making the proper changes to Sys Prefs > Sharing by following Apple's instructions to the letter, but the same thing happens: they never get the invite.
However, when we turn it around and they send me an invite to view their screen, it works, but of course it's not possible to control their screens and I have to go through the laborious, time-consuming process of "Click there, no, not there, to your left, etc.".
I have searched everywhere for an answer to this question but came up empty handed.
I wonder, could it be a firewall setting on their modems/routers that is preventing them from receving the invitation to screen share?
Please, can anyone help?

 

[sfx2000]

I will carefully walk these folks through the process of making the proper changes to Sys Prefs > Sharing by following Apple's instructions to the letter, but the same thing happens: they never get the invite.

Without stating the obvious - do they have Apple ID set up and logged in - needed for iMessage

It's not automatic

 

[SpeedThree]

You are right...I am dealing with a senior who may not have it set up properly. I will check with her over the weekend,

 

[SpeedThree]

Without stating the obvious - do they have Apple ID set up and logged in - needed for iMessage

It's not automatic

I have checked, via a Zoom session, the Messages settings of a fellow who never receives the invitations I send him and I can see nothing wrong with them. They are essentially the mirror opposite of my own settings, screen sharing is turned on, notifications in messages are turned on, he has only one AppleID, etc. Despite all this, my invitations to him are never received. Why is that about 10% of those with I try to screen share using Messages fail to receive the invite. So damn frustrating!

 

[sfx2000]

hmmm...

sometimes it helps to log out of imessage and log back in.

also - there was an issue if i recall, that was fixed with OS updates

BTW - if you have them on zoom, you can ask to get control there and look at things directly

 

[SpeedThree]

Thanks. I had him quit Messages & relaunch it.
We are both running the latest versions of Monterey.
It was on a Zoom session that we checked his Messages' preferences settings and they mirrored mine.
This really is a mystery as to why I can't get this to work w/ about 10% of the folks with whom I try it,

 

[SpeedThree]

I guess I give up on this one. I have tried everything:
• Quitting and restarting messages at both ends.
• Comparing my settings - which work fine with 90% of those with whom I screen share over messages - and everything in those settings looks fine on both ends.
• Tried, on the To: line using his iPhone number. Then queued up a new message and on the To: line put his @icloud address. Both failed in that he never received the invitation.