You cannot use a colon (:), a dot (.) or a slash (/) in an autosearch argument. These characters are used to distinguish an autosearch argument from a normal URL.
You can disable the autosearch feature if you don't like it.
Some example URLs for common search engines:
| DuckDuckGo | https://duckduckgo.com/?q=%s
|
| Startpage | https://www.startpage.com/sp/search?query=%s
|
You can easily find the URL for your favourite search engine if it isn't
listed above. Just do a search with the engine, then copy the URL of the
resulting page. Locate the search string you entered, it should appear
somewhere in the URL. Replace this search string by "%s"
(without quotes).