A site owner posted on the WordPress support forums with a problem that was driving them crazy. Their CF7 form was connected to Brevo using CF7's built-in integration. Contacts were being added to the Brevo list perfectly after every form submission.
Source: [Dev.to](https://dev.to/rahul_sharma_15bd129bc69e/cf7-brevo-integration-adds-contacts-but-never-sends-the-welcome-email-here-is-why-1e18)