Google+ invitation

Have you ever received a Google+ invitation?

Well, I didn't even know that there were invitations on Google+.
More, I didn't know any person, by default, could send you invitations for events or communities.

Everything started with this notification on my mobile:

Which look quite clear: somebody - that I don't know - invited me to something - that I don't know as well.
Ok, let's see what's that about... Top on it, Google+ app opening and... no clue: just the regular post stream of G+.

I haven't found any way to visualize what is this invitation about: a community? An event?

Ok, it is, probably, a limitation of the mobile app. Let's see on the web version... Same.

No way to find out who or what is this invitation about. There no way to visualize it - or at least I haven't found it.

So, looking around within the Google+ FAQ, there is this nice paragraph:

How can I control how many community invitations I receive?

You can control who is allowed to send you invitations as well as whether you receive invitations via email/mobile.
To control who is allowed to send you community invitations, visit the Google settings page and adjust the “Who can send you notifications” control.
To turn email and mobile notifications for community invitations on or off entirely, visit the Google settings page and toggle the “Invites me to a community” setting.

Note: Even if you have community invitations enabled via email/mobile, you won’t receive any invitations from people who you haven’t allowed to notify you.

It looks reasonable, even if nobody told me about that before.
Going to my settings page, Google+ section I can clearly see that everyone in the "Extended circles" can invite me.

Well, I don't know the guy who did invite, but he could be part of somebody else circle... but, then I find this.
Look the note at the very bottom page:

Note: In certain situations, you may still receive notifications from people outside the selected options, including information about photos and events that you created or attended as well as notifications from people who reach out to you via your email address.

Thanks Google to let everybody send me with spam invites.

But, believe or not, still no clue about that invitation: the only thing I have is that notification on my mobile.
Apparently the only way to verify that I've found is:

• Look for the guy who sent the invite
• On his page there was a post talking about a community with the same name of the invite
• Enter in the community with the "Community Preview" button
• Finally found the invite!

Easy right?

P.S. If anybody is aware of some other way to see received invites, you're very welcome to share this secret.