TestRail API call add_case, is not accepting my JSON -> error "invalid JSON parameter"

Question

I am trying to automate my QA process using n8n HTTP call to TestRail, everything works fine expect for 1 field which is not accepted. I don't know why.

This is my body below:

{
    "title": "This is a test case",
    "type_id": 1,
    "priority_id": 3,
    "estimate": "3m",
    "refs": "{{ $json.id }}",
    "custom_steps_separated": [
        {
            "content": "{{ $json.result }}",
            "expected": "Expected Result 1"
        }
    ]
}

Here is the guilty 'none valid JSON parameter:

{
"result": 
" Admins can access the space admins and can find the followings Evaluation settings to define data extraction templates"
}
]

If I kill the {{ $json.result }} it works perfectly.

I tried so many different scripts, what else I should do? Is there any testRail hidden restriction?