Fair play to Vimeo support, they have indeed whitelisted our Digital Ocean droplet IP address.
And in testing, the same URL as used in this thread, you’ll see it failed in all previous tests and worked perfectly on the last one just now:
Just to expand on this, I had to create a public post on our Discourse, with the failed embedded video URL visible and send them the URL to said post. I marked that post as unlisted.
I also had to verify that the IP address of our site was static (seemed an odd question).
And lastly, I had to provide a few paragraphs explaining what our intended use case was for wanting to embed videos in our site.
The whole process took just three days from start to finish 