Just a stab in the dark here.
It seems that you have extra square brackets. I think this is why your error message refers to field 0 -- you're sending it an array. Try it exactly as the article displays, with no square brackets?
For example:
"pass": {
"value": "test"
}
Good luck.
Update
To enable setting a password, you need to change a setting which is default in the install.
Go to admin/config/people/accounts (Configuration > People > Account Settings) and uncheck "Require email verification when a visitor creates an account":

Granted you are allowing POST to Anonymous users as described in the article above, you should be good to go and get a response such as the following in PostMan:
{
"uid": [
{
"value": "5"
}
],
"uuid": [
{
"value": "70738718-d4e9-455e-a1f6-cf95df613507"
}
],
"langcode": [
{
"value": "en"
}
],
"name": [
{
"value": "ac@bb.com"
}
],
"created": [
{
"value": 1487319576
}
],
"changed": [
{
"value": 1487319576
}
],
"default_langcode": [
{
"value": true
}
],
"user_picture": []
}
Hope this helps!!