Create the script to get the data form google sheets

AppsScript.gs

function doGet(request){

  //initialize the spreadsheet id
  var ss      = SpreadsheetApp.openById(''); //Fill the ID
  
  //get the column data
  var data = ss.getDataRange().getValues();

  //initialize the variable of 'data' rows
  var jsonArray = [];
  
  // loop the row data
  // the "var i = 1" because the data row is loop from second row,
  // the first row is just for labeling our column name in spreadsheet, like id, name and majors, so I start with i = 1
  for (var i = 1; i < data.length; i++) {

    //initialize the variable to wrap the whole of json output
    var jsonObject = {};
    
    //constraint the filled column from the first row(data[0])
    var colConstraint = data[0].length;

    //loop the col data
    for(var col = 0; col < colConstraint; col++){
      
      //first row should be like this :
      //col 0 {title : value [row i]}
      //col 1 {title : value [row i]}
      jsonObject[data[0][col]] = data[i][col];

    }

    //create an Array from Json Object
    jsonArray.push(jsonObject);
  }
  
  //checking the data, is empty or not
  if(jsonArray.length>0){
    var JSONString = JSON.stringify(
      { 
        'status': '200',
        'message': 'Success to fetch data',
        'data': jsonArray,
      }
    );
  } else {
    var JSONString = JSON.stringify(
      { 
        'status': '201',
        'message': 'Data empty',
        'data': jsonArray,
      }
    );
  }
  
  //create the json output
  var JSONOutput = ContentService.createTextOutput(JSONString);
  JSONOutput.setMimeType(ContentService.MimeType.JSON);
  return JSONOutput;

}