Before posting this question, I saw a similar question but disregarded it due to the fact that my API key with SendGrid was not changed or modified. I tried sending a test email and sure thing, it failed with the same error message as the one in log #2. Out of curiosity, I’ve decided to follow the instructions in the post mentioned earlier and set the API key again to the very same value it was always set to. And, surprise, surprise, it worked.
The only change that has taken place recently was me scripting the tenant with Auth0 Deploy CLI tool. So the question is, how did the API key for SendGrid got changed if I did not touch it? Is there a way to track it down?
Also, that error message could have been improved.