Create a new item with some columns values

Hello,

I’m trying to use the API to create new item to an existing board.
I used the create_item function found in the documentation, but unfortunately, my item was created but without the columns I provided.

Here’s my query

   mutation ($board: Int!, $col:JSON, $group: String) {
   create_item (board_id: $board, group_id: $group, item_name: "incieeedent test", column_values: $col) {
         id
     }
 }

And here how I passed my columns:

{
  ...
  "col": "{\\"Action\\": \\"foo\\"}",
  ...
}

If I try to remove the " then I have a 500 error status.

Any tips on how to send columns values?

Thanks!