Can I write to Google Sheet via Google Sheets API

Question

I am working on an app that reads and updates values in a Google Spreadsheet using Google Sheets API. I am able to read using my developer key, however attempting to write returns this error:

"Request is missing required authentication credential. Expected OAuth 2 access token, login cookie or other valid authentication credential."

Read (works fine):

$client = new Google_Client();
$client->setApplicationName("XXX");
$client->setDeveloperKey("XXX");
$service = new Google_Service_Sheets($client);
$spreadsheetId = "XXX";
$range = 'promocodes';
$response = $service->spreadsheets_values->get($spreadsheetId, $range);
$values = $response->getValues();

Write code (error):

$client = new Google_Client();
$client->setApplicationName("XXX");
$client->setDeveloperKey("XXX");
$service = new Google_Service_Sheets($client);
$spreadsheetId = "XXX";
$range = 'promocodes!C4';
$values = [1];
$body = new Google_Service_Sheets_ValueRange([
  'values' => $values
]);

$params = [
  'valueInputOption' => $valueInputOption
];
$result = $service->spreadsheets_values->update($spreadsheetId, $range,
    $body, $params);
printf("Cells updated.", $result->getUpdatedCells());

Answer 1

As I understand it, the Google API will allow you to read without an access token (using a developer key for credentials) however you can not update or add information without an oauth2 authentication method which involves sending credentials to google, receiving back a code from them, using that code to get an access token, then using that access token as your credentials to add or update information.