I have an internal WordPress site that I’m trying to embed via iFrame. Currently I’m stuck on

Error: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.

I have set the following in wp-config.php:

define( 'WP_SAMESITE_COOKIE', 'None' );

And added the following to my .htaccess:

<IfModule mod_headers.c>
    Header set Access-Control-Allow-Origin https://parenturl.com
    Header set X-Frame-Options ALLOWALL
</IfModule>

Header always edit Set-Cookie (.*) "$1; SameSite=None; Secure"

But still no success — any suggestions?