I had similar issue. The question is quite old, but anyone looking for apt answer can see this.
Do not pass "/" for rewrite slug, since it causes more problem than it solves, as in this case, causing 404 error in other pages.
First, we need to remove the slug from the URL for the published post. Paste the code in functions.php
/**
* Remove the slug from published post permalinks. Only affect our CPT though.
*/
function sh_remove_cpt_slug( $post_link, $post, $leavename ) {
if ( in_array( $post->post_type, array( 'product-type' ) )
|| 'publish' == $post->post_status )
$post_link = str_replace( '/' . $post->post_type . '/', '/', $post_link );
return $post_link;
}
add_filter( 'post_type_link', 'sh_remove_cpt_slug', 10, 3 );
This will still cause error since it specifies that only 'post' and 'page' post types can have url without post-type slug.
Now to teach WP that out CPT will also have URL without slug, we need to get this in our functions.php
function sh_parse_request_tricksy( $query ) {
// Only loop the main query
if ( ! $query->is_main_query() ) {
return;
}
// Only loop our very specific rewrite rule match
if ( 2 != count( $query->query )
|| ! isset( $query->query['page'] ) )
return;
// 'name' will be set if post permalinks are just post_name, otherwise the page rule will match
if ( ! empty( $query->query['name'] ) ) {
$query->set( 'post_type', array( 'product-type' ) );
}
}
add_action( 'pre_get_posts', 'sh_parse_request_tricksy' );
This is it. Ref: https://wordpress.stackexchange.com/a/320711/98322