You can upload the plist in your intranet so your QA can access it.
It is important to have HTTPS, otherwise iOS won't download the IPA. If you don't have an HTTPS server with a certificate in your intranet you can use a third party service, like Dropbox.
You need the distribution manifest only if you want to automate the build via script, if you export from Xcode you only need to upload the IPA and the Plist
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