Error "Precondition check failed"

[Cooya]

I am using googleapis to send emails on behalf of my customers. It works fine for most customers but for one in particular, I get the following error :

Error: Precondition check failed.
    at Gaxios._request (/home/nicolas/mi/node_modules/gaxios/build/src/gaxios.js:84:23)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async OAuth2Client.requestAsync (/home/nicolas/mi/node_modules/googleapis-common/node_modules/google-auth-library/build/src/auth/oauth2client.js:343:18)
    at async Object.sendEmail (/home/nicolas/mi/src/utils/google_api.js:53:4)
    at async Object.sendEmail (/home/nicolas/mi/src/utils/email_manager.js:264:3)

After a few searches on the web, I found out that this error is related to service accounts, but I am not using service accounts, I am authenticated with OAuth.
So what could it be ? Does it has to do with the type of Google account my customer owns ?

The code of my method for sending emails :

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

async sendEmail(credentials, to, subject, message, options) {
    const oauth = new google.auth.OAuth2(config.oauth_client_id, config.oauth_client_secret, `${webConfig.hostname}/mon-compte`);

   // set the user credentials
   oauth.setCredentials(credentials);

   // build the email
   const raw = buildEmail(to, subject, message, options);

   // send the email
   await google.gmail({ version: 'v1', auth: oauth }).users.messages.send({
      userId: 'me',
      resource: { raw }
   });
}

[Cooya]

Is anyone there ?