Fill PDF Smart Service Add Image to Image Field

I am using the Fill PDF Smart Service from the PDF Tools plugin. I have a fillable PDF with an image field that I am trying to insert an image into. The image is stored in the knowledge center. I have the PDF Field value in the data tab set as such. 

{
    {"name": "image", "value": todocument(pv!documentId)
    }
}

However, it is not filling the field and there are no errors when running the process for debugging. Please advise.