Hello,
I have the same problem. I cannot "Save" (upload). I get a CORS error in the console. Maybe it has something to do with that.
Access to internal resource at 'https://gdtf-share.com/landing/pages/login.php?builder=true' (redirected from 'https://fixturebuilder.gdtf-share.com/manifest.json') from origin 'https://fixturebuilder.gdtf-share.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
createGdtf:1
Failed to load resource: the server responded with a status of 502 (Proxy Error)