As another user (jmooring) mentioned, we are now in the beta 1 stage for Ubuntu 18.04 LTS (the release candidate comes out in five days). Your package that you have marked as being for 18.04 is the same as the package marked for 17.10 (the filename includes artful, not bionic). This package will install and run on 18.04, but when you try to install the companion package (insync-nautilus, insync-thunar, insync-nemo, etc.) or whenever you run apt-get update you get an error message because the bionic repository on apt.insync.com/ubuntu is not yet ready.
I would suggest that you coordinate your timing of updating these repositories with the beta 1 milestone if you can’t follow the recommendation of jmooring to emulate the way Google does this. This is a big release; when you include all of the Ubuntu flavors along with the fact that many other distributions (Mint, KDE Neon) base on the LTS version of Ubuntu, a lot of your users are going to be having problems. It would be really nice if this could happen in the next week, prior to the RC becoming available.