This issue is not directly related to Bookly but appears to be linked to the latest WordPress version 6.4.3. You can find more information about this issue here https://core.trac.wordpress.org/ticket/60398
To resolve the issue, you can install Bookly Pro (Add-on) archive or any other Bookly add-on via ftp, or we can assist with this matter. Please reach out to us via support@bookly.info, provide access to your WP admin panel and we'll help.