Plex friends invites disappearing into the ether?

Hello i have been with Plex for a couple of years only using it locally at my home. I recently - about 5 months ago - paid for Plex Pass and have successfully invited a few friends. I tried to invite another friend this past weekend and she claimed to never get the email invite. So I redid it double checking her email address and resent it. On a lark I also setup and sent an invite to a gmail account that I have personally but never use except for spam signups etc. Well one hour later she never received the email invite (checked her email address and her spam folder) and I never got the email either in my gmail account.
I know how to do this as I have already done it a few times before. There were no errors when I sent out either invite. Is there some sort of limit on “friends” accounts?
I have invited 4 other people.
thanks.

You haven’t reached the friend limit, yet.

Do it this way:
Let your friend create a Plex account on their own, by “signing up” on the plex.tv homepage
https://www.plex.tv/sign-up/

Once they have this account created and their email address verified, invite them by their plex username.
They can then go and accept the invitation not only by clicking a link in their email (which might get lost in the spam filter), but also after logging in on the plex.tv website.
https://support.plex.tv/hc/en-us/articles/201161077-Accept-an-Invitation

Yes, how Otto describes is usually how i do it, ask them to create a user first.
Then the invite appears in their notifications on plex.tv

Thanks guys. I was totally away from this forum and will try your advice.