On a local copy of seriouslybonkers.com / bigram.co.uk the following message appeared in the Chrome console
Mixed Content: The page at 'https://qw/bigram/bigram/sales-blurb/' was loaded over HTTPS,
but requested an insecure script
'http://qw/bigram/wp-content/plugins/oik-ajax/js/oik-ajax.js?ver=4.9.7'.
This request has been blocked; the content must be served over HTTPS.
On a local copy of seriouslybonkers.com / bigram.co.uk the following message appeared in the Chrome console
The script should be enqueued using https.