On Android platform, streamingAssets is place inside APK file.
Like this: "jar:file://" + Application.dataPath + "!/assets".
The recommend way to load those assets by Unity is to use UnityWebRequest to send a request to download a file.
I try to replace the UnityWebRequest directly by using the Best/Https's HTTPRequest, but seems HTTPRequest is not support the scheme "jar:file://" and return errors.