Your old password could still be saved in your internet browser. Try to enter your password manually, if you still can’t sign in you’ll need to clear the data so you can use your new password. Once you’ve done this, close your browser and reopen it.
If you have a user ID with your invitation, it should ask you to sign in. If not, you’ll have a link to create one with the email address the invite was sent to. After you create a user ID, you’ll be able to sign in.