Hi Anastasiia.davydiuk,
Firstly ,please check operating System and Browser
Requirements for Microsoft Lync Web App.
You could change another browser (Firefox) and make a test.
If you use skype for business server ,you could use skype for business web app plug-in
Please update SFB server to the latest version.
Try to re-install the Lync web app plugin in Mac OS , you could refer to
this link.
Best Regards,
Leon Lu
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