Adding Json data in a variable in ROBOT framework - testing

Question

I am starting to work on automating API requests using ROBOT framework and came across the below issue.
I have this JSON data
{
"password": "123456789",
"username": "test#test.com"
}
I want to put the above in a variable and generate a token as a response.
Previously I had used the below
${body}= create dictionary username=test#test.com password=123456789
I got the below error response
HTTPError: 415 Client Error: Unsupported Media Type for url:
Can someone help me on this please.
Updated Code
*** Settings ***
Library String
Library Collections
Library RequestsLibrary
*** Variables ***
Credentials
${prod_url} localhost:3000/api
*** Test Cases ***
User login and token generation.
Create Session demo ${prod_url}
${body}= create dictionary username=test#test.com password=123456789
${header}= create dictionary Content-Type=application/json
${login}= post on session demo /login data=${body} headers=${header}
log to console ${login.content}
Above is full code. What I need is the username and password needs to be in JSON format because My API is accepting only those values..

Answer 1

Instead of the data argument, try passing the dictionary to the json one:
${login}= post on session demo /login json=${body}
headers=${header}
When you use the data, the library passes as-is the string representation of the object - and in python a str of a dict is {'password': '123456789' ,... - e.g. it uses single quotes, not double ones, which is an invalid json.
Passing the dict to the other argument, json, will make it convert to the proper format.