WordPress multisite child theme showing as broken theme

I am using wordpress with multisite enabled. Now I took bootstrap _tk theme as parent and made a child theme named as _tk child theme. So basically I have defined the theme name in child theme like this

/*
 Theme Name:     _tk Child Theme
 Theme URI:      http://www.example.com/
 Description:    _tk Child Theme
 Author:         Example 
 Author URI:     http://www.example.com/
 Template:       _tk
 Version:        1.0.0
*/

@import url("../_tk-master/style.css");

But when I went to the wordpress dashboard theme section. I can’t see the theme. Then I went to dashboard network section( as I have enabled multisite) there I can see under the section Broken Theme the _tk Child Theme is placed. I have tried both network enabled and disabled for the parent theme but I can’t see the child theme working. So can someone kindly tell me what’s the issue here? Any help and suggestions will be really appreciable. Thanks