Sound problem in programmed meetings

Hello,

I experience sound problems when I schedule a meeting: I can't hear de the participants AND the participants can't hear me BUT they can hear each other! 😳

When I simply send the link to my meeting room, everything works perfectly fine. 

What am I doing wrong when scheduling the meeting. I've done it before without experiencing any problem.

It is really annoying and looks so unprofessional !

Thanks for the help