How to Decode & Map JSON Objects using NewDecode, Golang and req *http.Request

Coming from PHP I'm a TOTAL Golang newb here. I read a question that is VERY similar to mine but my implementation is slightly off. Whenever I go to decode using the following code the variable msg.Username is always blank. Golang doesn't throw errors here so I know I'm missing something super small here and very important but I have no idea what it could be. I would be a very appreciative of any help and am of course expecting this to be a fist-to-foerhead epiphany. Thanks! Coming from PHP I'm a TOTAL Golang newb here. I