I opened a support ticket on this over a week ago (#65512 ) and I haven't heard back. Here's what I wrote for that ticket (names and email addresses removed for privacy):

Hello. My husband and I have family sharing turned on with the Apple App Store. As you probably know, this means that all purchases go through one person's credit card, which happens to be mine. Together we sat down to upgrade his old MSecure to Msecure 5. Things didn't go well. We paid full price for the app through the app store, but it didn't work. His "Trial Status" refused to clear, so we thought the purchase had failed (also because there was no sign of the purchase on my credit card or on the app store for my account at that time.)  After a couple of failed tries, we went to your website. There, we discovered that we could pay you directly. My husband did this (using our shared credit card over Apple Pay), and it worked great. His login credential immediately got associated with the payment and he got full access to the app. Unfortunately, a day later the App Store purchase finally showed up on our credit card. So...now we've been charged twice, once through the app store for 29.99 and again through "Paddle.net" for 14.99. [I included with my support request] a copy of the email confirmation that you sent to my husband's email address. How do we resolve this? Can you refund either of these purchases for us? Do I need to have him contact you directly?

Thank you for your reply. I did process a refund request through Apple. Hopefully this won't affect my husband's access to his full version in the meantime. If it does, I'm assuming we'll be able to iron out the registration issue later  with a little help at your end. I'll encourage him to make a backup in any case, and we'll see what happens.

Enjoy the holiday weekend!