After downloading the Flipbook Extension, open the package.
If you purchased Single Package :
You will see there is a file : mod_flipbook.zip
Upload the files to your site using the Joomla Installer.
You can find the Joomla Installer in the admin area of your Joomla website,
link : administrator/index.php?option=com_installer&view=install
You will receive a success message after successful installation.
Now you can start the installation of the extension.
Go to Plugins section and make a search for Flipbook
Joomla PWA extension is compatible with Joomla 4 and Joomla 3
You can install the same package on both Joomla 3 and Joomla 4.