Yeah, I think you’re misunderstanding my situation.
As I wrote, I’ve already got finished Sender Authentication of Sendgrid with my SUBdomain. I registered MXrecord of SUBdomain also. And it fully works when using bubble API plugin until now.
The problem is, Bubble does not verify my sendgrid key because I used subdomain to be authenticated in Sendgrid.
My root domain doesn’t need sendgrid and I don’t want to send email with my root domain. But bubble requires to authenticate root domain in sendgrid EVEN THOUGH I use subdomain.