Good evening Barry.
Thank You for having a look at this, and taking the time to reply. 
I had already tried your suggestion, and it hadn’t worked for me.
I get a blank screen, with no errors in the web console.
The amount of things I have tried would be too extensive to list here, but I Do apologise for not mentioning the basic iframe string, in that format. 
After reading your post, and knowing that I’ve tried that, I thought there may be something mis-configured within my setup, but I tried it in the codepen link within my primary post, and it also returns a blank screen, as displayed in the attached images below.
Without string
With string
If You or Another have any further suggestions, and/or questions, they will be welcomed, and Greatly appreciated.
Thank You once again Barry 
Kindest Regards