unexpected error - h5p generated iframe embed code in Drupal 8

The H5P module is installed on Drupal 8.5.6 (theme used is a Barrio Bootstrap 4 subtheme)

The H5P module is creating and saving content without issues. However, after taking the embed code using the h5p embed button, the following error is the result once the code is placed in a document (locally and on other domains):

'The website encountered an unexpected error. Please try again later.'

The url included in the iframe uses the following path:
our-domain/h5p/133/embed

The default h5P package path was automatically set at installation and is 'h5p' which is present at the end of the sites/default/files path.

Sample urls were taken from h5p.org and a WordPress example for comparision:
https://h5p.org/h5p/embed/612

Both worked and have a different structure - 'embed' is before the file reference - not after.

Changing /embed and the reference around directly in the iframe code results in a different error message - the full page loads with the following:

'The requested page could not be found.'

The second url in the embed code for h5p-resizer.js is OK and displays the correct file.

The problem is how to confirm if the path for the content is the issue (and how to fix it), or if there are other configuration issues to consider.

I'm new to Drupal, so any guidance is much appreciated.