Download Enterprise IPA file from web server - ios

Question

I have seen a few similar questions but they are all several years old and largely unhelpful.
I am hosting a few enterprise apps on AWS S3 and am trying to correctly create the manifest file. When the app is downloaded I am using a presigned URL to get the manifest.plist file which looks like the following:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>items</key>
<array>
<dict>
<key>assets</key>
<array>
<dict>
<key>kind</key>
<string>software-package</string>
<key>url</key>
<string>**S3 URL**</string>
</dict>
<dict>
<key>kind</key>
<string>full-size-image</string>
<key>needs-shine</key>
<false/>
<key>url</key>
<string>**S3 URL**</string>
</dict>
<dict>
<key>kind</key>
<string>display-image</string>
<key>needs-shine</key>
<false/>
<key>url</key>
<string>**S3 URL**</string>
</dict>
</array>
<key>metadata</key>
<dict>
<key>bundle-identifier</key>
<string>com.iOS.app</string>
<key>bundle-version</key>
<string>1.6.3</string>
<key>kind</key>
<string>software</string>
<key>platform-identifier</key>
<string>com.apple.platform.iphoneos</string>
<key>title</key>
<string>appName</string>
</dict>
</dict>
</array>
</dict>
</plist>
All of the URL's in the manifest.plist are currently public to help with testing, so if you go to any of the URL's directly the file is downloaded in the browser correctly.
The URL generated by the download is
itms-services://?action=download-manifest&url=https://{S3Bucket/Key}?AWSAccessKeyId={KEY}&Expires=1636478776&Signature={Signature}&x-amz-security-token={token}
With the actual URL's and token omitted.
I have tried this version and also added amp; after the "&" as suggested in this post Downloading App update OTA from Amazon Aws s3 iOS
In both versions of the download URL I am prompted to "Open In Itunes" but nothing happens when I click "yes".
Are there any updated hints or something I am missing?
Any help would be much appreciated.