This does not match what you are testing: 
https://github.com/sebmartel/s2g-server/pull/10/files#diff-af6863705393b4784dde01a685ca1767L209:
```PUT #/accounts/:username/facebookId```
but instead:
```PUT #/accounts/:username?facebookId=...&username=...```

Let's go with the first form plz.