When we were flying home from Portugal 3 weeks ago, our negative covid test results were only on our phones, no paper copy. We flew on Air France. 24 hours before flight time, I'd gotten the emailed reminder to check in, and I was able to do that, but when I tried to upload travel documents to Fly Ready, as suggested in the email, I like you got the message that it wasn't available for my destination. No problem, we were going to have to go to the check in desk to check luggage anyway. The Air France agent had no issue with the fact that we were showing her our results by phone instead of giving her a paper copy. I had the whole email opened up. My husband had zoomed in on the QR code but she told him that didn't work, she had no way to scan that and needed to see the whole email. Quick and easy. It's frustrating that the Delta Fly Ready app is so touchy. It worked for us once, traveling back from Italy in November, but more typically we get the error message.