Uploading File Attachments on Monday.com Board via API

Hello there @Amrutha and welcome to the community!

I am not familiar with Power Automate, but I wonder if the issue might lie in the body. I see you are passing multiple headers with different content types. I do not know how that works in Power Automate.

For reference here is a working example on a column (it works basically in the same way):

curl --location 'https://api.monday.com/v2/file' \\
--header 'Authorization: APITOKENHERE' \\
--form 'query="mutation add_file(\\$file: File\\!) {add_file_to_column(item_id: 1234567890, column_id:\\"files__1\\" file: \\$file) {id}}
"' \\
--form 'map="{\\"image\\":\\"variables.file\\"}
"' \\
--form 'image=@"/Users/matias/Documents/myDocument.xlsx"'

JS:

const myHeaders = new Headers();
myHeaders.append("Authorization", "APITOKENHERE");
const formdata = new FormData();
formdata.append("query", "mutation add_file($file: File!) {add_file_to_column(item_id: 1234567890, column_id:\\"files__1\\" file: $file) {id}}\\n");
formdata.append("map", "{\\"image\\":\\"variables.file\\"}\\n");
formdata.append("image", fileInput.files[0], "myDocument.xlsx");

const requestOptions = {
  method: "POST",
  headers: myHeaders,
  body: formdata,
  redirect: "follow"
};

fetch("https://api.monday.com/v2/file", requestOptions)
  .then((response) => response.text())
  .then((result) => console.log(result))
  .catch((error) => console.error(error));