posting data successfully arrives, but word doc not populated

HI,

Below is my JSON code that im posting to the /convert/template/to/docx API.

The request generates a word document as needed, however, my document doesnt populate with the contents of the JsonPayload.

I'm expecting to see Acme Product appearing in my word doc. but the variable remains unchanged

Variable as defined in the word doc is

${ProductName}

Have also tried {{ProductName}}

Am i missing something?

        "Parameters": [
            {
                "Name": "File",
                "FileValue": {
                    "Url": "https://voicebox.spencr.com.au/temp/mm-default-letter-head-2025-test.docx"
                }
            },
            {
                "Name": "JsonPayload",
                "Value": 
                            '[   
                                {   
                                "Name"  : "ProductName",
                                "Value" :"Acme Product",
                                "Type"  : "string"
                                }   
                            ]'
            },
            {
                "Name": "FileName",
                "Value": "daves-test-file"
            },
            {
                "Name": "StoreFile",
                "Value": true
            }
        ]
    }