Just to be clear, this still could just be a problem on your Mac.
But something else you’re doing here… GET requests normally don’t have content in their body. Usually you would do a POST or PUT for that.
I guess so, but if Postman works and URLConnection does not, then I’m thinking it’s URLConnection.
Do me a favor and check to make sure that postman isn’t changing the method to POST or PUT when you have content.
Postman does not change the method
You confirmed that on the server right ?
Also try Greg’s suggestion of a GET with no body (as it’s supposed to be)
It shows GET in Postman’s log and also GET in the web app’s logs.
You given this a go ?
Not yet - I am about 100 miles away from my computer right now 
Can you try to manually type everything into the sendsync? Don’t copy paste, it could be the url that’s malformed or something.
How long is your url?
it’s not the URL