I've joined the 3 mile weekend challenge last feb 12-14 but unfortunately it was not syncronised by my Vivomove & did not get the badge
What I meant is it is not recorded the km I've walked during the day of Feb 12-14.
I am sorry, but if the activity was not recorded, you cannot get the badge, even if steps were recorded that day. If you have a Walking activity of 3 miles or more, then please share a link to it, so that we check it out.
Did you join the challenge before doing the walk? Challenge badges are not being awarded automatically, unless you opt for participating on the respective Challenge. It is easiest done on the web interface at https://connect.garmin.com/modern/challenge
There are some issues with really old devices that only saves in TCX file format, but vivomove was launched in 2016 so that shouldn't be the issue here.
Could you post a link to the activity so we can look at it? Browse to it in Garmin Connect Web: [https://connect.garmin.com/modern]. Copy the URL and post it here. It is a good idea to put the link between square brackets [ ] since there is an issue with links in the forum. Make sure that you make it public by clicking the pad lock in the upper right corner.