@ntozier I have now reinstalled osTicket and manually (1.11.0-rc1 to 1.10.1).
Although I had to set up one or the other new, but now everything works.
Nevertheless, thanks for the answers.

@jumboteam Thank you, it works interestingly way
Maybe it has something to do with the new installation ?

Alright, I've already tried the whole by mail function to install, but works only semi-good.
osTicket only receives e-mails from the same server (for whatever reason) and sending replies by e-mail does not want to work at all.

Hi Guys,
when I respond to a ticket and this sender I always end up on the Error 500 page.
The answer will still be stored correctly in the database.

Apache2 Error Log after sending the ticket: https://pastebin.com/suzc0N7V

osTicket Information: https://i.imgur.com/7JLCdT0.png

I would like to install a function on the website domain.tld with which one can report members and thus an osTicket is created.
The tickets are only visible on support.domain.tld.

That's my current problem.
And the script I received from you tells me to change the URL on line 18. The URL points to support.domain.tld/api/tickets.json where osTicket is located, but it does not want to work.

Hi Guys,
I have no idea how to use PHP and the API to create a ticket.
The /api/tickets.json does not exist with me either.

I hope you can help me with this.

Best regards,
Justin