Bulk insert from one table to another

Well, I’ve managed to make it work, but IN POSTMAN:

In Glide, it gives the following error:
“Unexpected token in JSON at position 2”
Clearly, it’s telling me that my JSON is malformed, right? That’s what I thought, so I started testing in POSTMAN and exactly the same JSON could add a row correctly to my native glide table. It returns 200 OK and the new rowID

Let me explain how I form the JSON in Glide:

1- I form the “mutation” ( I took from the Add Row example of the table where I want to make the insertion) with a template column:

2- In another table, I call that column “mutation” using a Single Value link

3- In a column of type template (called body), I add the App Id and below it the mutation

It look like this

For me is the same that I write in POSTMAN I don’t know why is not working

4- In the CALL API, I place the headers and the body.

What could it be? Is some column adding unwanted characters to my JSON?
@ThinhDinh @Darren_Murphy

Why are you using a single value column here though? Not that it directly is the cause, but I thought you should be using a lookup here.

Any reasons you don’t use a JSON column to create this here, but a template column?