You can not use an External Launch function unless a Form.com mobile application is installed on your device.
Please use the links below to download and install the application:
The Form.com Mobile application can be installed on the iPhone, iPad and iPod from the iTunes App Store.
The Form.com Mobile application can be installed on Android devices from the Google Play Store.
If an Universal Links feature has been accidentally disabled for the application on iOS (the application is installed but does not open via link), please tap and hold the respective link below and select the particular application from the menu shown. This will enable Universal Links feature again.
Form.com Mobile - select 'Open in 'Form.com''