Event Tickets Plus: Issue with Ticket / Data entry / email problem

We have the problem that we ask for individual attendee data (name and email) during the ticket purchase so that the email dispatch works. Since these fields are optional, we can not ensure that the data is specified. If we make the function subscriber data required (mandatory field), then, for example, with two tickets can not be used the same email.
But there should be the possibility that the email can be used multiple times. What do we have to change to avoid this? (Event tickets Plus – ticket settings)

The automatic sending of tickets by mail does not work either, we always have to go to the backend and click on resend tickets to make it work. We also already use a SMTP server from Sendinblue our newsletter plugin. And the tickets always end up in the spam folder.

The check in with the APP (Appname) does not work either, here always comes this card is not authorized to check in. Can it be that you can check in tickets only on the day of the event?

Furthermore, we want that customers can buy tickets without registration, for this we have created an extra now ticket button in the list. (see https://www.roterhirsch.com), unfortunately this does not work yet.

We have been waiting for an answer for a week now and hope for a quick response.

The page I need help with: [log in to see the link]