Thanks for the quick reply!
The QR code is indeed one generated by Blynk, from my iPhone 5S. I have successfully shared it with a few friends already, two on iOS (iPhone 5S & 6), and one on Android (Google Pixel).
However, another friend with a Samsung Galaxy S5 has been unable to scan it. There is no error message or any indication that anything is wrong–the app simply does not acknowledge the code. The image when we try to scan is well lit and very sharp, and the phone was not shaky, and we have tried varying the distance from the phone to the code as well.
I have not tried generating a different QR code within Blynk, as this is the only app I have built so far, and I wasn’t sure if re-generating the code for the same app would impact the access I have already given to my other friends.
I wish I had more diagnostic info to provide, but that’s all I’m able to observe–the scanner just acts as if it does not see a QR code in view.
Thanks for your help.