Spot Check

If it won't let you in

It asks you to sign in

That's normal. Use the Google account whose address was added for you — it has to be that exact address.

"You don't have access"

Your address hasn't been added yet, or you signed in with a different one than the one on the list.

It won't load at all, or shows an error page

Something in the plumbing has fallen over. Nothing you did, and nothing you can fix from your end.

Who to tell

Any of the above, email rastermonkey@gmail.com. Say what you saw on screen and roughly when — that's usually enough to find it.