I tried another approach, which was defining my protocol in my content security policy header: Content-Security-Policy: connect-src myapp:; script-src 'unsafe-inline' And then calling fetch() on "myapp://". Safari shows an error on this: Refused to connect to "myapp://rest of the url>" because it does not appear in the connect-src directive of the Content-Security-Policy I've tried Content-Security-Policy: connect-src myapp:; script-src 'unsafe-inline' Content-Security-Policy: connect-src myapp:; script-src 'unsafe-inline' Content-Security-Policy: connect-src myapp://; script-src 'unsafe-inline' Content-Security-Policy: connect-src myapp://*; script-src 'unsafe-inline' None of these work, but do produce different errors.

An interesting update. I just noticed that the bottom of my swcutil text output from sysdiagnose has a SINGLE entry in the SETTINGS section, and it looks like it is explicitly not allowing my app to launch. It says: =================================== SETTINGS =================================== { s = applinks, a =<my fully qualified app bundle id>, d = (null) }: { "com.apple.LaunchServices.enabled" = 0; } This is in contrast to a device where it is working correctly. On that device is have MANY entries in the SETTINGS section, including: -------------------------------------------------------------------------------- { s = applinks, a = <my fully qualified app bundle id>, d = (null) }: { "com.apple.LaunchServices.enabled" = 1; } So, I guess the question now is - how is this flag set - is this something done by user behaviour, or some other side effect? One for the DTS engineers I think!

I'm aware of the tap and hold - however, in my case choosing "Open in [App Name]" does nothing. My app doesn't get launched, and there is nothing in the log to suggest that there was any failure; My app isn't launched and immediately crashing ; the menu item appears to do nothing.