Can't send an email from service account, get 400 Precondition check failed error

Question

Trying to send an email using a service account with role owner within my project. I keep getting a 400 error that says Precondition check failed.

const sendEmail = async () => {

const auth = new google.auth.GoogleAuth({
    keyFile: "gmail.json", //the key file
    scopes: "https://www.googleapis.com/auth/gmail.send",
});

const authClientObject = await auth.getClient();
const gmail = google.gmail({version:"v1", auth: authClientObject})
  // Compose the email
  const email = 'To: [email protected]\r\n' +
                `Cc: [email protected]\r\n` +
                'Subject: CUSTOM DONATION ALERT\r\n\r\n' +
                'blablabla\r\n';
  
  // Encode the email in base64 format
  const base64EncodedEmail = Buffer.from(email).toString('base64');
  
  // Send the email
  gmail.users.messages.send({
    userId: serviceAccountEmail,
    resource: {
      raw: base64EncodedEmail,
    },
  }, (err, res) => {
    if (err) {
      console.error('Error sending email:', err);
      return;
    }
  
    console.log('Email sent:', res.data);
  });

}

Answer 1

Precondition check failed.

Normally occurs when you are using a service account and have not properly configured domain wide delegation within your google workspace account.

I can also see you have not denoted which user in your workspace account the service account should delignate as.

const {google} = require('googleapis');
const path = require('path');

async function runSample(impersonate) {
    // acquire an authentication client using a service account
    const auth = await google.auth.getClient({
        keyFile: path.join('C:\\Development\\FreeLance\\GoogleSamples\\Credentials\\workspaceserviceaccount.json'),
        scopes: ['https://www.googleapis.com/auth/gmail.readonly' ],
        clientOptions: { subject: impersonate },
    });

    // obtain the gmail client
    const gmail = google.gmail({version: 'v1', auth});


     // Lists the messages in the user's account.

    console.log(auth)
    const res = await gmail.users.messages.list({
        userId: 'me',
    });
    const messages = res.data.messages;
    if (!messages || messages.length === 0) {
        console.log('No messages found.');
        return;
    }
    console.log('messages:');
    messages.forEach((message) => {
        console.log(`- ${message.id} - ${message.subject}`);
    });
}

runSample('[email protected]').catch(console.error);