I was invited to a website and I didn't receive the invitation

Hi there. I’m on a team where each of us handles a subset of websites, but we want to have access to all of them collectively. I was able to invite others to my websites, but every time they send me an invitation to their sites, I receive nothing. I don’t get it neither on my email account, nor on CF dash.

I have activated the 2FA for my sites, and so they did (or at least most of them). We tried doing this many times, from many people in the team, and none succeeded.

Which could be the problem?