Website adress

Hello, In the main template settings Moto3 is a box where I write the Web address. Unfortunately, once you write your web address that is www.tanecni-vecery.cz write it alerted "Value is not a valid URL", but the address is entered correctly and with that address, I do not authorize Save Settings. So I have to write the address www.tanecni-vecery.com that could save the settings. What should I do, so I went to fill out the correct address? Thank you very much.