How to invite others

I run Slackware-14.2/x86_64. I created a meeting and sent the URL <<meeting_name> to a colleague. I sent that URL to a colleague (who runs windows10 on his laptop). We both logged in using that URL and found we were each the sole attendee in that meeting. Apparently, two copies of the meeting, one for each of us.

I tried the ‘invite others’ options on the meeting page but one froze my desktop so hard I had to reboot it. The ‘copy to clipboard’ may have worked but I’ve no idea where the clipboard is so I could not retrieve it. And, when I tried copying the URL it showed up briefly at the bottom of the page but disappeared when I tried to highlight it to copy elsewhere.

What did I do wrong?