curl --request POST \
  --url https://api-v2.missioninbox.com/users/ \
  --header 'Content-Type: application/json' \
  --data '{
  "username": "<string>",
  "email": "jsmith@example.com",
  "first_name": "<string>",
  "last_name": "<string>"
}'

{
  "id": 123,
  "username": "<string>",
  "email": "jsmith@example.com",
  "first_name": "<string>",
  "last_name": "<string>"
}