@bubble, the documentation and/or API used for Sendgrid Templates needs updating. It appears you’re using V2 (now labeled Legacy Templates), instead of the new default for SendGrid, which is V3 (a.k.a Dynamic Templates).
I was trying to apply a template to the system emails (password reset, etc.) that Bubble sends by specifying a template ID, but I encountered an issue where once I apply a template ID, then the subject/body text does not show in the emails I receive due to you using V2 templates/API and me using V3 templates.
Ideally, we need a way to setup the substitution variable(s) (i.e. handlebar syntax) for the system emails.