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One user reported that turning off his VPN then installing the extension from the Epic Webstore worked. So please make sure Epic's encrypted proxy and any VPN on your system are all turned off before installing an extension.
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There is a solution. This seems to happen when in the settings you've chose a folder for downloads to be saved to...we're not sure why. Please change the settings to allow Epic to save Downloads to the usual place then try again and it should install. Then you can revert the settings back to save downloads in the location of your choice.
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