Thank you @melliesou
Setting the option ID (first field) to a number has solved my issue.
So I have enabled all department, product and priority fields and made them mandatory for the ticket form.
I have the following options (left) with the test values (right):
Department: тест; маркетинг;
Priority: приоритетно; нормално;
Product: сајт; панел;
Thank you very much for the quick response
