Access denied for h5p content (iframe)

Dear all,

On my WordPress site I have created some h5p quizzes I’d like to embed to other pages outside the site domain. Other users tell me that this is not a problem at all, but on my pages I get the error message that the origin/source website has declined the access. I tried embedding the code on one of my other WordPress pages, but get the same error message. I've checked the plugin settings and also tried to grant access by changing the .htaccess file by adding

Header always unset X-Frame-Options

Header set Content-Security-Policy "frame-ancestors 'self' https://*"

Still I get the same reply, the access is denied by the source/ origin page.

Thanks for your help, Sandra