Ubuntu installation procedure doesn't work for Server 5.5

This is what happens:

[snip]

root@ubuntu-xenial:~# curl -O http://packages.couchbase.com/releases/couchbase-release/couchbase-release-1.0-6-amd64.deb
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 4996 100 4996 0 0 27373 0 -::- -::- -::- 27450
root@ubuntu-xenial:~# dpkg -i ./couchbase-release-1.0-6-amd64.deb
Selecting previously unselected package couchbase-release.
(Reading database ... 204433 files and directories currently installed.)
Preparing to unpack .../couchbase-release-1.0-6-amd64.deb ...
Unpacking couchbase-release (1.0-6) ...
Setting up couchbase-release (1.0-6) ...
gpg: keyring `/home/vagrant/.gnupg/secring.gpg' created
gpg: keyring `/home/vagrant/.gnupg/pubring.gpg' created
gpg: /home/vagrant/.gnupg/trustdb.gpg: trustdb created
gpg: key CD406E62: public key "Couchbase Release Key (RPM) <support@couchbase.com>" imported
gpg: key D9223EDA: public key "Couchbase Release Key <support@couchbase.com>" imported
gpg: key 79CF7903: public key "Couchbase Builder Key <support@couchbase.com>" imported
gpg: Total number processed: 3
gpg: imported: 3 (RSA: 2)
OK
root@ubuntu-xenial:~# apt-get update
Get:1 http://packages.couchbase.com/releases/couchbase-server/enterprise/deb xenial InRelease [3,337 B]
Get:2 http://packages.couchbase.com/releases/couchbase-server/community/deb xenial InRelease [2,957 B]
Get:3 http://packages.couchbase.com/ubuntu xenial InRelease [3,007 B]
Hit:4 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:5 http://archive.ubuntu.com/ubuntu xenial InRelease
Get:6 http://packages.couchbase.com/releases/couchbase-server/enterprise/deb xenial/xenial/main amd64 Packages [3,411 B]
Hit:7 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Get:8 http://packages.couchbase.com/releases/couchbase-server/community/deb xenial/xenial/main amd64 Packages [1,581 B]
Get:9 http://packages.couchbase.com/ubuntu xenial/xenial/main amd64 Packages [1,433 B]
Hit:10 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Fetched 15.7 kB in 0s (20.7 kB/s)
Reading package lists... Done
root@ubuntu-xenial:~# apt -y install ./couchbase-server.deb
Reading package lists... Done
E: Unsupported file ./couchbase-server.deb given on commandline
root@ubuntu-xenial:~# apt install ./couchbase-server.deb
Reading package lists... Done
E: Unsupported file ./couchbase-server.deb given on commandline
root@ubuntu-xenial:~# apt install couchbase-server.deb
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package couchbase-server.deb
E: Couldn't find any package by glob 'couchbase-server.deb'
E: Couldn't find any package by regex 'couchbase-server.deb'
root@ubuntu-xenial:~# apt install ./couchbase-server.deb
Reading package lists... Done
E: Unsupported file ./couchbase-server.deb given on commandline

[snip]

Thanks for reading