Hello! I wanted to share my work which spent some time and patience.

I tried a lot of format that returns multiple errors. I also got an idea from someone here in the community but I forgot the name. Well, thanks to you.

Hope this helps! Happy coding!

This results to:

{“query” : “mutation { create_item (board_id: 3063556967, item_name: "Daily xxx" , column_values: "{\\"date\\" : {\\"date\\" : \\"2022-08-15\\"}}"){ id} }”}

Remember the escaping.