1) Check Ad Url - For demo not found ad URL - https://in.nearmeads.com/kochi/data-science-course-in-kochi/your-ad-title_i1234
Replce or change manualy ( _ underscore to - hyphen ( dash) )
New Correct Ad URL - https://in.nearmeads.com/kochi/data-science-course-in-kochi/your-ad-title-i1234
hope this changes work & show exists active ad here.
After changing URL from _ to - in last ad id still ad not found then might be ad removed / spam / unblock or its not active.
Check ad category , you can find all active ads there
Either something get wrong or the page doesn't exist anymore