How Do I Set Up the E-Mail SMTP Server Required for Discourse?

[Lilly]

i don’t know anything about brevo but if you use the search feature you can find topics about it

Discourse notification e-mail sending with Brevo(Sendinblue)

These are the official guides from Brevo: Fairly simple process to set DKIM, DMARC and DNS records for mail sub-domain to authenticate mail and sender.

are you doing a standard install?