Hey Jean, Product Manager for SendGrid here. I wanted to let you know that everything that you are trying to accomplish should be done with API Keys. We released our API Keys functionality three years ago as a more secure way to manage your applications interaction with SendGrid. The problem with using Teammates (credentials) four your apps authentication method is that you can also use them to log into your SendGrid account, which is not ideal. When users were utilizing their credentials for both API calls and account management, resetting your password meant that they were breaking their mail send integration. Teammates is really about user management, not application management. Please reach out to me if you have any questions, Jensen.Stava@sendgrid.com. Here is the link to documentation on how to get started with API keys:

Guide:

Classroom:

https://sendgrid.com/docs/Classroom/Send/How_Emails_Are_Sent/api_keys.html