Looks like it was in March. No confirmation, but a few articles.
https://www.newsweek.com/russia-nato-ukraine-command-center-strike-kinzhal-missile-1791805
https://www.algora.com/Algora_blog/2023/04/16/the-catastrophe-of-nato-forces-in-ukraine
https://www.easternherald.com/2023/03/31/russian-aerospace-forces-eliminated-up-to-200-foreign-officers-with-a-kinzhal-strike-on-a-nato-communications-center/