Input byte array has incorrect ending byte at 40

Okay, I found out. The original String is encoded on an Android device using android.util.Base64 by Base64.encodeToString(json.getBytes("UTF-8"), Base64.DEFAULT);. It uses android.util.Base64.DEFAULT encoding scheme.

Then on the server side when using java.util.Base64 this has to be decoded with Base64.getMimeDecoder().decode(payload) not with Base64.getDecoder().decode(payload)

I was trying to use the strings from the args. I found that if I use arg[0].trim() that it made it work. eg

Base64.getDecoder().decode(arg[0].trim());

I guess there's some sort of whitespace that gets it messed up.