Forms do not work with https

I’m using Mautic with WordPress. I’m unable to display any forms due to a mixed content warning:

Mixed Content: The page at ‘https://example.com/instructor-signup/’ was loaded over HTTPS, but requested an insecure script ‘https://mautic.example.com/mtc.js’. This request has been blocked; the content must be served over HTTPS.

I have updated all my config URLs and redirect URLs with https. However, I am not able to locate the mtc.js script. Regardless it seems this is a bug that should be fixed.