I was able to resolve the issue. It appears MFA was not enabled for this account, so the conditional access policy was blocking it. I added MFA, and all is good.
I have run into another issue, though. I am now attempting to set up SMTP for outbound. I select "Same as remote mailbox" and when I click submit, I receive the following error:
Service with name "osTicket\Mail\Protocol\Smtp\Auth\OAuth2" could not be created. Reason: No wrapper found supporting "UTF-8"
Any thoughts?