Similar things happen with me too.
I have 4 website in cyberpanel with 2-2 email account each.
I use brevo SMTP in cyberpanel but cyberpanel give me option to put only one as global SMTP relay via terminal, which work for my all 4 domain.
I setup my all four domain to that single brevo account so it’s working.
But I want to use multiple SMTP brevo account for my multiple domain because
There is a limited number of mail I can send from single brevo SMTP account.
If I can use multiple brevo account for each domain.
Then I can get 300/day email limit for each domain.
Right now I have 300/day email limit in total for all my 4 domain.