"https://api.instagram.com/v1/tags/{tagname}?access_token=abacdefg223bjdh"
its give the error message like
This request requires scope=public_content, but this access token is not authorized with this scope. The user must re-authorize your application with scope=public_content to be granted this permissions.
IN SANDBOXMODE ITS NOT GIVE ANY PERMISSION
You must add the scope when you're requesting the token. You can refer to this answer here: Adding scopes to instagram app?