Download the ZIP package file of Akeeba Backup Professional from our site.
Install it twice in a row, without uninstalling it before or in between. This will reinstall the package contents, including the Backup On Update plugin.
Now check that the plugin is installed and enabled (published). Because what we were doing with the double installation is technically an "update", not a clean installation, as far as Joomla! is concerned the plugin will have been installed but may not have been enabled.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!