And one more question about custom fields:
We have created a selection field and would like to fill it (automatically) with data from another application. What are the recommended options I have for this (database, API, Ruby script) and do you have examples/documentation for an implementation?
Where are the custom fields (User, ticket, group etc.) You can fill custom fields via API. Select the corresponding endpoint, make a GET-Request and you will see your custom fields. With a PUT-Request you can update them. Don’t manipulate the database!
Thanks for the hint - had also found it shortly after my question and then still searched for {id} in GUI. But now everything is clear. Thanks again for the clarification with the database.