I followed the instructions for installing insync on Ubuntu from the repository…
$ cat /etc/apt/sources.list.d/insync.list
deb http://apt.insync.io/ubuntu HirsuteHippo non-free contrib
and I added the public key…
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys ACCAF35C
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
Executing: /tmp/apt-key-gpghome.TMe3Oilt8t/gpg.1.sh --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys ACCAF35C
gpg: key A684470CACCAF35C: “Insynchq Inc services@insynchq.com” not changed
gpg: Total number processed: 1
gpg: unchanged: 1
But when I do apt-get update…
Hit:1 https://download.docker.com/linux/ubuntu hirsute InRelease
Hit:2 http://dl.google.com/linux/chrome/deb stable InRelease
Get:3 http://security.ubuntu.com/ubuntu hirsute-security InRelease [101 kB]
Hit:4 https://packages.cloud.google.com/apt cloud-sdk InRelease
Hit:5 http://au.archive.ubuntu.com/ubuntu hirsute InRelease
Err:6 http://apt.insync.io/ubuntu HirsuteHippo InRelease
403 Forbidden [IP: 52.217.102.228 80]
Hit:7 http://au.archive.ubuntu.com/ubuntu hirsute-updates InRelease
Hit:8 http://au.archive.ubuntu.com/ubuntu hirsute-backports InRelease
Reading package lists… Done
E: Failed to fetch http://apt.insync.io/ubuntu/dists/HirsuteHippo/InRelease 403 Forbidden [IP: 52.217.102.228 80]
E: The repository ‘http://apt.insync.io/ubuntu HirsuteHippo InRelease’ is not signed.
N: Updating from such a repository can’t be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.