I can’t upload theme

Hi. Please help. I’ve purchased a new theme & every time I try to upload, it says
The package could not be installed. PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature
My plugins are updated. I have opened the zip file & selected *style* rather than trying to upload the whole file but neither are working.
I’m quite new to this so please simplify your reply if possible!

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