Template is missing. Standalone themes need to have a index.php template file. Child themes need to have a Template header in the style.css stylesheet.

In WordPress themes showing error like : Broken Theme as below :

Template is missing. Standalone themes need to have a index.php template file. Child themes need to have a Template header in the style.css stylesheet.

 

This is because of your child theme missing,  Template Name is missing from the style.css

Add this line to your child theme css, with parent theme name

Template: twentyfifteen

eg:

/*!Theme Name: mytheme

Theme URI: http://vinshakp.com/

Author: vinsha

Template: twentyfifteen

*/