I've just installed the Font Awesome plugin to help speed up font display on my site and it has two instances of font awesome listed for the Product Slider plugin?
It also has them listed as 'Unregistered Clients' and suggests:
'Contact the developer for the unregistered client and ask them to consider updating their code to register with this Font Awesome Official plugin. Let them know they can reach us at firstname.lastname@example.org.'
Here's the link to the font awesome plugin: https://wordpress.org/plugins/font-awesome/
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Thanks for the reported issue, i will fix and update plugin.