3D FlipBook - Hello. I have successfully used your great flipbook plugin on my wordpress site but it stopped working today. Perhaps not

Hello. I have successfully used your great flipbook plugin on my wordpress site but it stopped working today. Perhaps not coincidentally, my web host upgraded the PHP version on my development site to 7.3. The PDF no longer displays on the page it was on, though the div shows up in the source code. When I go to edit the PDF in the plug-in, I get the following error message in the Details area: “Sorry something went wrong with the server please try again.” The same error message appears on the Shortcode Generator page. I can send screenshots if that will help. The page on my development server is https://dev-sheltermedicine.pantheonsite.io/shelter-medicine-times-newsletter-v4-i1/ and on the live server, which does not have the latest PHP as far as I know, is https://www.sheltermedicine.com/shelter-medicine-times-newsletter-v4-i1/ . My purchase was from 13 Feb 2019. Thank you.