Hello Jared, thanks for reporting this!
We have updated this post accordingly. However, we don’t have a Mailtrap plugin for WordPress — we know there is a couple of plugins on their marketplace but they are not official.

you are a life saver. thank you

The PHPMailer library just got a major update, going from version 5.2.27 to 6.1.6.

This broke the mailtrap plugin due to class reference

public function mailer_setup(PHPMailer $phpmailer)

Needs to be update to

public function mailer_setup(PHPMailerPHPMailerPHPMailer $phpmailer)

While I found this in a plugin it also applies to the above function reference