Recently we started getting IPN failure notices

Recently we started getting IPN failure notices from PayPal, which by the way ended up being erroneous we believe. During troubleshooting I changed our current IPN URL in our PayPal account to a new address and their system forced me to use HTTPS. Afterwards I tried to switch it back to the original URL which we see on our Membership --> Payment Gateways --> PayPal Payment Standard --> Settings as --> http://dentalqualityassurance.com/paymentreturn/paypalexpress/

But their system would not allow us to change it to anything that was not HTTPS. After a multi-hour support call and terminal hold, we were told that recently their system was updated and now requires HTTPS and that if you edit the IPN URL it will force HTTPS from that point forward. That explained why we worked this morning before changing it and are now broken and cannot revert. Afterwards we expressed our extreme displeasure with their support the manager we ultimately talked to, of course that fell on deaf ears. So now we are coming to WPMUDEV to see if you guys can help us resolve this by changing to HTTPS.

So our question is, how do we get that URL to be HTTPS instead of HTTP in the membership system so we can align properly to PayPal's requirements?

Thanks