Site in subfolder problem

Hi, great plugin. I do have a problem though in that a site that i’m adding the plugin to is in a sub folder. It causes a problem with the download link as it has the subfolder in the url ie
http://www.website.co.uk/subfolder/?voucher=8ac3bbe14f089150711782d1c6be75ef&guid=3a40663284bf0bbcf0c033560aecf853
This them means that when you click on it you get a “This webpage is not available ERR_INVALID_RESPONSE” page
I guess its because the WordPress Address (URL) still needs the full url in order to work. If I remove the subfolder from the url it does download (although I do get a Failed to load PDF message and the downloaded pdf says it is damaged).
Do you know any way of changing the download URL not to show the subfolder?

Thanks

https://ww.wp.xz.cn/plugins/voucherpress/