Are you aware that in the Proton Mail PLUS account you are allowed 10 email addresses (on top of the primary one) and not only 5 as you indicated in the lesson? This may have changed since you wrote this topic in the course.
ProtonMail added proton.me several months after Glen made his video. With 5 protonmail.com addresses and 5 proton.me addresses, there are now 10 useable addresses.