Passwordless flow: What to do when user enters an invalid email when logging in

I’m planning to make my app passwordless and I’ve seen sites implement things differently when one puts in an email they haven’t actually used for an account on the site before when trying to login.

On Medium, if I put in a new email I’ll get the message “We just emailed a confirmation link to youremail@gmail.com. Click the link to complete your account set-up.”

This makes the signup process fast, but I’m not sure if this message is strong enough to make it clear to some users that this was a new email being used. This could frustrate users who had forgotten which email was used for their existing account and would now take the time to realize they’re using a new account before trying to login again with the right email. However, that scenario may not occur often enough that its worth designing the UX to prevent it.

Zeit does design things so if I don’t have an account and I put in a new email I’ll get the message “There is no ZEIT account associated with this email address. Continue with signup?” and I can click to signup.

This prevents one from realizing they used the wrong email, but it adds an extra step to signing up and I think it could confuse users who weren’t paying attention to the fact that they clicked login rather than signin.

What do you think is a better flow and why?

Can a character with the Polearm Master feat make an opportunity attack against an invisible creature that enters their reach?

The second benefit of the Polearm Master feat (PHB, p. 168) says:

While you are wielding a glaive, halberd, pike, quarterstaff, or spear, other creatures provoke an opportunity attack from you when they enter your reach.

The regular rules on opportunity attacks state:

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.

Obviously, Polearm Master lets you use your reaction to make an opportunity attack when a creature enters your reach, in addition to the opportunity attack any character can make when a creature leaves their reach. However, does the opportunity attack from Polearm Master follow the same restriction on needing to see the creature, or can this attack be made even without seeing the creature that enters its reach?

If an invisible creature enters the reach of a character with the Polearm Master feat, can the character make an opportunity attack against that creature?