You get it wrong. I didn't create or use child template. Please read more about child templates in the docs.
Again, you don't have to create a template or use a child template. You can do everything in single post to /api/report.
In the limited way it looks like this:
{
"template": {
"recipe": "phantom-pdf",
"engine": "none",
"content": "<img style='display:none'... />",
"phantom": {
"header": "<img ... />"
}
}
}
If you would really want to use child templates. You need to first create a template using OData POST.
https://jsreport.net/learn/api#create
