Brevo, formerly known as SendinBlue started the official deprecation of their API v2 in June 2020 and deprecated it completely in December 2022.
SendinBlue API v2 or Brevo API v2 is deprecated!
Thrive Themes is compatible with the API v3 and can be integrated easily. Here is a document on how you can connect Thrive Themes with Brevo using their latest API version.
If you’d like to know more about this transition, Brevo has an article where you can read more.