I have read the relevant FAQ and my uddeIM shows
"Configuration is writeable: /administrator/components/com_uddeim/config.class.php"

My Joomla is totally updated and there are no other issues.

Nevertheless, when I click on "Save" button in the uddeIM configuration page, nothing happens. Is there some other issue I could check out?

Thank you, Melki

Maybe an compatibility issue with the template?

Please check:
www.joomlapolis.com/forum/25-uddeim-plugin-and-component/229254-nobug-template-problem-uddeim-not-working-with-341-jumla

Super!

Yes, the interface was set to Hathor, and when I changed it back to Isis, the problem went away. Thank you for your super fast help!

Melki