problems with mendeley libre office 6.2.8.2

Hi! I have installed mendeley 1.19.4 in ubuntu 18.04. When I open Libereoffice wirter (6.2.8.2) to add citation, bibliography, choose citation style, etc. nothing seems to work. Then when I checked at the extension manager of Libereoffice writer I found a problem Error: The status of this extension is unknown. Can somebody help?