I am using YourPorter. Just downloaded your new app.
I tried to follow the steps described in your link, and entered a shared calendar I created with yourporter that has only the guest name (mandatory), dates, & phone number in it. Nothing else.
But I get an error message saying “No reservation data available in custom calendar response from xxx”
I am a little doubtful that YourPorter is exporting the calendar in an iCal format. Maybe this is the problem?
On YourPorter, I followed these steps: Menu > Share Calendar > Create a Link to Share > Phone Number > and I received a link in the format http://pform.us/abcd