When you see a link or a code snippet that starts with something like itms-services://?action=download-manifest&url=, it's typically used for downloading manifest files directly from a server, usually in the context of iOS or iTunes services. The amp-url part could imply a parameter for specifying an Accelerated Mobile Pages URL.
When using in a shell script or email client that supports raw URIs, use: Itms-services Action Download-manifest Amp-url Https
Important note: In some documentation (or malformed copies), you might see amp-url. This is not a separate parameter. It is an HTML entity encoding error where & becomes & amp; (without space). Correctly parsed, amp-url is simply &url. We will address this common typo later. itms-services : This is the protocol iOS uses
itms-services: This is the protocol iOS uses to recognize that an installation is being requested, rather than a standard webpage.action=download-manifest: This tells the system to look for a plist file containing installation instructions.url: This parameter (missing from your snippet but implied) provides the link to the XML content shown above..ipa file).amp instead of & or a copy‑paste error)..plist files from AMP URLs, but the parameter would still be url.amp tracking parameter.