How can I make basic writing via Google Sheets API?

As @sam-berlin mentioned I should have used fetchObjectByUpdatingObject instead of fetchObjectByInsertUpdating.

But there was one more little mistake/typo. In constructing JSON I lost a pair of square brackets and got an error about invalid value.

The working code looks like this:

func constructAndSendARequest() { let baseUrl = "https://sheets.googleapis.com/v4/spreadsheets" let spreadsheetId = "1FhbBdEvpsfgzb3Akn1opmru0iresdfglbki5ZMmZaRs" let range = "Sales!A3:D3" let url = baseUrl + "/" + spreadsheetId + "/values/" + range let params = ["valueInputOption": "RAW"] let fullUrl = GTLUtilities.URLWithString(url, queryParameters: params) let body = GTLObject() body.JSON = ["range": range, "majorDimension": "ROWS", "values": [["One", "Two", "Three"]]] service.fetchObjectByUpdatingObject(body, forURL: fullUrl, delegate: self, didFinishSelector: #selector(ViewController.processTheResponse(_:finishedWithObject:error:))) } 

It's also possible to use service.fetchObjectByUpdatingObject(body, forURL: fullUrl, completionHandler: nil) and not process the response.

According to the GTLService code, fetchObjectByInsertUpdating does a POST, whereas this request requires a PUT. It seems that fetchObjectByUpdatingObject should do a PUT, so try that instead.

If someone needs, I answered here on the similar question. You can use the GTLRSheets_ValueRange() object and GTLRSheetsQuery_SpreadsheetsValuesUpdate.query(withObject: to create or update any cell through Google Sheets API.

let service = GTLRSheetsService() service.authorizer = GIDSignIn.sharedInstance().currentUser.authentication.fetcherAuthorizer() service.apiKey = Constants.GOOGLE_SPEADSHEET_API_KEY let rowIndex:Int = job.rowIndex let range = "Employee List!C\(rowIndex):C\(rowIndex)" let valueRange = GTLRSheets_ValueRange() valueRange.range = "Employee List!C\(rowIndex):C\(rowIndex)" valueRange.values = [[job.jobTitle!]] valueRange.majorDimension = "COLUMNS" let query = GTLRSheetsQuery_SpreadsheetsValuesUpdate.query(withObject: valueRange, spreadsheetId: Constants.SPREAD_SHEET_ID, range: range) query.valueInputOption = "USER_ENTERED" service.executeQuery(query) { (ticket, response, error) in print(response) }