Block Design not downloading - blocked by CORS policy

Hi!
One of my clients was trying to add a page to his WordPress site and informed me that he can't use pre-made block designs as nothing is happening when he selects one.

So I investigated myself and noticed that, no matter what hosting (I also tried on locally hosted sites I use for development) browser, device or version of the Nicepage plugin, the issue can be easily and consistently replicated. I decided to test with the Nicepage desktop app and there is no issue.

Using my browser's console, I found this error message every time (this one if from my localhost dev site):

/wordpress/wp-admin/edit.php?post_type=page&ver=5.9.6&page=np_app#/builder/1/page/122:1 Access to XMLHttpRequest at 'http://editor.nicepageapp.com/d2cc3eaa/1546336/PreviewWithStyle/Page-11_152635520.html?version=f4a8ac91-a594-4797-a30d-c5f0000b6ace&_=1697191162036' from origin 'http://localhost' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

And just below the following:

Failed to load resource: net::ERR_FAILED editor.nicepageapp.com/d2cc3eaa/1546336/PreviewWithStyle/Page-11_152635520.html?version=f4a8ac91-a594-4797-a30d-c5f0000b6ace&_=1697191162036:1

Thanks for helping.

Best
Olivier