Embed code does not work

Hello. I created a dialog card and the embed iframe code works well on another site. The display embed setting was set to 'only for editors'. I then created an accordion, a true / false and another dialog card but the embed codes have not worked for any of them. The error message reads: 'content unavailable.' I have changed the display embed setting to 'always' but still the embed codes do not work for them. The embed code for the first dialog card still works. I am using wordpress 4.9.6

Please advise. Many thanks.