Envato Market Plugin Failing to Activate

I have successfully used the Envato Market Plugin for dozens of sites except for one. It is the largest site I manage so was thinking there could be a plugin conflict as I’ve downloaded the plugin about 10 times now thinking there was something wrong with the download. So, I installed on a new site and it worked fine.

The error message says: "Envato Market plugin is not installed correctly. Please delete this plugin and get the correct zip file from https://envato.com/market-plugin/."

Is there a list of known plugins that conflict during install? I am using Salient on this site. Thank in advance!

I am not sure and it should not happen. maybe in your installation files are missing/corrupted. please can you delete the plugin and try to upload the plugin using ftp/cpanel. Also please make sure your website wp version, php and theme all are up-to-date. Thanks

I updated to latest PHP version, deactivated 4 plugins but no luck. Will try to ftp it now and reply with result. .

OK so finally had a chance to FTP it into the site and am getting the same exact error message. It says its been installed fine and only get the error message when trying to activate it. Ive turned off nearly all the plugins, updated PHP all with no luck.

Any other ideas? Its worked on all but this website and unfortunately this is probably the most important one.