setRequestProperty throwing java.lang.IllegalStateException: Cannot set request property after connection is made

This usually happens if you have in the debug watchers calls, such as conn.getResponseCode() or anything that queries the request result before the request was actually issued or completed. This causes, that during debug, a request is performed by the watcher, before having properly set you request, and then it becomes invalid.

I only have this issue while in debugging mode, Run without debugging (You can print logs) everything should work fine

The obvious thing is to think that you need to add properties before calling open on the URL. this however is not the case. i have seen many samples of settings being set AFTER url has been open (as counter intuitive as that is).

the problem in my case is that i had conn.getResponseCode() added in my watch list. removed that and all good.

... tricky.