"It's not you, it's us" when accepting IAM Identity Center invitation

Hello, I was following the tutorial https://aws.amazon.com/getting-started/guides/setup-environment/module-two/ on creating IAM Identity center users. I started it yesterday, created a user, assigned a group, then I received email with invitation. When I clicked I was asked to choose MFA, which I didn't want yet, so I closed the browser tab. Today, I continued the tutorial with adding permission sets to that administrative user. But when I now open the invitation I get: "It's not you, it's us We couldn't complete your request right now, please try again later". Of course, later is no better. So maybe it's me, after all.

1. How can I recover from that? Should I delete the user and create again?
2. Is MFA mandatory for administrative users created that way? When the invitation was showing me the MFA options, it was stated that my AWS organization requires MFA. But it was me, who created that AWS organization, so I should be probably able to turn it off. The tutorial implies it's mandatory though.