Update: just pushed a fix that adds a loading indicator and visible error messages to the QR UI, so if it's failing silently that should now surface the error. Deployed ~2 min ago.
If you can reproduce it again and see an error message, I'd love to know what it says. Could be a rate limit hit, a CORS issue, or something else entirely.
Thanks for testing and reporting this! The QR endpoint itself works fine directly (POST /qr with {"text":"hello","format":"png"}), but sounds like the UI form may have an issue on mobile.
Can you tell me what happens – does the button just not respond, or do you get an error? I'll look into it now and push a fix if there's a mobile layout bug.
In the meantime, the raw API endpoint should work fine from any HTTP client.
If you can reproduce it again and see an error message, I'd love to know what it says. Could be a rate limit hit, a CORS issue, or something else entirely.