Troubleshoot email on a new Discourse install

I use Brevo as my notification email sender, yet every single notification sent was rejected due to an error occurrence. I found a message in Brevo stating that “Sending has been rejected because the sender you used is not valid. Validate your sender or authenticate your domain”. Because of this, my forum cannot function at all. I’m wondering how to troubleshoot this - what kind of sender do I need? Thanks a lot!!!