@rfc2822 thanks for this feedback
Here is a summary of what I found:
URL prefix in QR code: webcal:
ICSx5 installed already?: No
Result: “Sorry, the requested application could not be launched. The barcode contents may be invalid”
URL prefix in QR code: webcal:
ICSx5 installed already?: Yes
Result: the button says “Open in browser” but it actually opens ICSx5 correctly
URL prefix in QR code: http:
ICSx5 installed already?: Yes
Result: the button says “Open in browser” and it goes to the browser, not ICSx5
Conclusion: I think it is probably best to use http:// URLs in the QR codes. Server-side script can see if the Accept: header includes text/calendar and either return the calendar or display a help page with both a clickable webcal: link and also a download link for ICSx5. I’ll publish an example later.
