I am using siducation (debian sid) and when I try to the pair the request expire. Both desktop and android phone can find each other but when I try to pair on clicking the notification (on both the case) the request finish without any alert. I see only that they saw each others. I don't have any error printed and I am not sure where to check for a log. Ref: https://www.reddit.com/r/linux/comments/9bkcup/kde_connect_ama/e54cder/?context=10000
There is the firewall on the router but I guess that if was blocking something the pairing with the notification should have problems as well.