The first attempt to install Plesk on a Linux server using Web Installer was interrupted for some reason (for example, the Web Installer tab was closed or the SSH connection to the server was dropped).
The server was re-deployed or reset to the initial state (in which it was prior to the first attempt) and its IP address remained the same.
New attempts to install Plesk on this server using Web Installer do not start with the error:
PLESK_ERROR: Installation to the host 203.0.113.2 has been already started.
#PPPM-11275 "Installing Plesk via https://get.plesk.com no longer fails with the “Installation to the host has been already started” error if there has been an aborted or unsuccessful attempt to install Plesk on a server with the same IP address in the past."
- Plesk Obsidian 17 March 2020 (Linux)
If update is not possible for some reason you may try the following
Until the bug is fixed, install Plesk using any other method besides Web Installer which are described in the article How to install Plesk for Linux