When required fields are missed on the ticket submission form and submission fails, have a more obvious failure message generated for the user at the top of the page. Alternatively re-position the screen over missed field(s).
Make missing required fields more obvious - Phản hồi / Feature Request - Deskpro Support
Make missing required fields more obvious Collecting Feedback
"There are errors with the ticket fields that you must correct before replying."
which doesnt inform you which field has not been filled out.