plugins - Custom Post Type Front Page Gives 404

I have developed a plugin on one site and just now moved it to another. At start I had that problem in the initial site too. Saving permalinks again solved it in the initial website.

I then moved it to the new website and I am getting it again. I tried to save the permalinks settings again but it isn't helping.

I saw multiple solutions but none solved the issue.

This is how I create the custom post type:

register_post_type( 'ossp',
    array(
        'labels'       => array(
            'name'       => __( 'Sale Page' ),
     ),
     'rewrite' => array( 'slug' => 'sale-page', 'with_front' => false ),
     'public'                   => true,
     'hierarchical'         => true,
     'has_archive'          => true,
     'publicly_queryable'   => true,
     'supports'     => array(
         'title',
         // 'page-attributes',
         'editor',
         'excerpt',
         'thumbnail',
        ),
    )
);

If any more information is needed, tell me and I'll edit the question.

Thanks!