Sorry for the late replay.
1) Please, open "Talk" module from the portal and check errors in the browser console (F12)
2) Does the desktop client work properly?
3) Please, provide us jabber log-files via e-mail email@example.com
and please insert the link to this thread into your email or you may attach them here. You may find logs here: c:\Program Files\Ascensio System SIA\ONLYOFFICE\Logs\