Unable to write through service account access in google spread sheet api (node js)

Question

I have a google sheet and I am able to read from google sheet by giving access to service account. Below is the snippet of code for reading.

 // configure a JWT auth client
let jwtClient = new google.auth.JWT(
    privatekey.client_email,
    null,
    privatekey.private_key,
    ['https://www.googleapis.com/auth/spreadsheets',
     'https://www.googleapis.com/auth/drive']);
//authenticate request
jwtClient.authorize(function (err, tokens) {
if (err) {
console.log(err);
return;
} else {
console.log("Successfully connected!");
}
})

    // getting data from  google sheet
sheets.spreadsheets.values.get({
   auth: jwtClient,
   spreadsheetId: spreadsheetId,
   range: range
}, function (err, response) {
   if (err) {
       console.log('The API returned an error: ' + err);
   } else {
    console.log('Users list from Google Sheets:', response.data.values);
    
   }
});

this works perfectly, and i am getting the data. But when I want to write to google sheet, it gives an error. Snippet of writing

//  writing to google sheets
let values = [
    [
      'abc','b.ed'
    ],
  ];
  const requestBody = {
    values,
  };
  sheets.spreadsheets.values.update({
    spreadsheetId,
    range:"Sheet1!C3",
    valueInputOption,
    requestBody,
  }, (err, result) => {
    if (err) {
      // Handle error
      console.log(err);
    } else {
      console.log('%d cells updated.', result.updatedCells);
    }
  });

The error I am getting

GaxiosError: Login Required. at Gaxios._request (/home/spread sheet auth (node js + service account)/node_modules/gaxios/build/src/gaxios.js:129:23) at processTicksAndRejections (node:internal/process/task_queues:96:5) { errors: [ { message: 'Login Required.', domain: 'global', reason: 'required', location: 'Authorization', locationType: 'header' } ] }

Answer 1

Lets look at the working example you have

sheets.spreadsheets.values.get({
   auth: jwtClient,
   spreadsheetId: spreadsheetId,
   range: range

Notice how you have added auth and set it to your jwtClient? This adds the authorization permission to your call.

Now lets look at your update statment

sheets.spreadsheets.values.update({
    spreadsheetId,
    range:"Sheet1!C3",
    valueInputOption,
    requestBody,

You have not added auth, which means you are trying to preform this action without being authenticated. Update acts upon a users private data you need permission to be able to call this method.

So by that logic the following should fix your error

sheets.spreadsheets.values.update({
    auth: jwtClient,
    spreadsheetId,
    range:"Sheet1!C3",
    valueInputOption,
    requestBody,