This is visible here:
When limit is reached:
This article of our help center gives more details: https://help.brevo.com/hc/en-us/articles/360022153079-Are-there-any-sending-limits-emails-and-SMS-
If you hit the daily limit, you will be able to manually send your email to all your contacts on the next days thanks to the Requeue feature. You can also upgrade your plan to remove this daily sending limit.