-d doesn't work (questions)

[HappyGitHubUser]

I'm trying to make a request like:

wfuzz -c -z file,user.txt -d "{"client_id":"xxxxx","username":"FUZZ","password":"superpassword","realm":"xxx-yyy","credential_type":"http://yy.com/xx"}" https://xx.yy.com/co/authenticate

and I'm just received 400 code, probably because my -d it's wrong, when I research how to use -d, I just found payloads like:

wfuzz -c -z file,user.txt -d "username=FUZZ&password=superpassword" https://xx.yy.com/co/authenticate