Unable to submit final materials in LOA4 - cross-post

Cross-posted on Administration Forum.

I've been trying to submit my final course materials in LOA4 but have been unable to. These materials include one mp3 with both study songs and one with all other materials and also the test pdf. Each mp3 is about 7.5MB. Unfortunately, try as I might the system just seems to hang and I get the following message:

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Secure Connection FailedAn error occurred during a connection to www.bluesharmonica.com. PR_CONNECT_RESET_ERROR    The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.    Please contact the website owners to inform them of this problem.

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I've tried this on both Firefox v.81.01 and Safari v.13.01.02 on an iMac running High Sierra. Please advise as to what I should do.