zoom link problems

[derman]

I have a Pro work subscription. I am the host, and send the meeting link by E-Mail to the meeting partners. Out of 25  meeting participants, 3 get the link on their inbox mail , as a black link, while it should be blue. The black link does not allow them to enter the zoom meeting. Have you encountered such a link appearance?  What could be the reason for it? How can it be fixed ?