key not found and unauthorized with sendinblue

Ok so I am trying to set up this plugin for use with sendinblue. I actually need to make sure it doesn’t override our default email service which is through gmail. I am just trying to send out an email to admins whenever a comment is made and held for moderation, because we moderate the blog.

So the test email is getting successfully sent but when i make a comment it is erroring to this and only emailing the error to the main admin email:

You getting this message because an error detected while delivered your email.
For the domain: https://mydomain.org
The log to paste when you open a support issue:
[400] Client error: POST https://api.sendinblue.com/v3/smtp/email resulted in a 400 Bad Request response:
{“code”:”missing_parameter”,”message”:”Either of htmlContent or textContent is required”}

also: {“message”:”Key not found”,”code”:”unauthorized”}

Outside the “set up in under a minute” video I havent really found step by step instructions. I made the API key in sendinblue but did not verify the domain yet. I also have not changed the outgoing mail server from gmail to sendinblue. I’m not sure if this is causing the issue or not. I’m being careful because I only need this certain functionality and checking the boxes under “email me whenever” in wordpress admin section is not working.

Are there some other steps I need to take? Will this mess with our actual gmail email settings?

Welp! Thanks for any advice!