I've managed to workaround it by creating a User-Defined Setting THE_OFFENDING_URL that contains the URL value, and using ${THE_OFFENDING_URL} as the value of NSAdvertisingAttributionReportEndpoint in the plist. Of course, this will only work if you have option "Expand Build Settings in Info.plist File" set to true in your Build Settings. I've also opened a ticket through Feedback Assistant because this is obviously a Xcode bug.

@robnotyou I'm not entirely sure what you're referring to. My plist looks like this: and source looks like this: As you can see, the value is not unterminated. Also, even if the value wasn't complete, Xcode should close the value with a anyway, which is what is making me think that this is a bug in Xcode (there might be a way to workaround this escaping the slashes, but not sure how to do it).