Last week i thought i couldn’t join the halo 3 flight, but today i received a message that i, indeed, received the flight but didn’t answered, but still got time to enter, i checked my notifications and messages, there’s nothing there, i can’t join the flight but the system told me i received the invitation, what can i do?
EDIT: Just after posting this received the invitation!
Same exact thing for me; I have the email telling me to check for two messages for instructions and that I was invited a week ago but I have no email in my spam or inbox and no messages or notifications
*Literally the same exact thing as op; as soon as I posted I received the invite
Just got the same email but with no messages anywhere to join the flight 
Hey folks, feel free to keep an eye on this thread though notifications should be rolling out to everyone
https://www.halowaypoint.com/en-us/forums/243780d3b80b4bb6ac7917a8942286db/topics/got-the-invite-but-no-msg-or-notification/c756d39e-ab7e-475f-96f7-f46e0dd64b84/posts
If you’re having trouble accessing the Insider support site, try the main URL:
https://insidersupport.halowaypoint.com/