Hi,
Thanks for using our plugins. I can help out here.
The link does not have to have a specific ending, but it does have to be in the iCal format.
I tested the link, but on my shared hosting it was not able to load all the events so the server that reads it would have to be more powerful.
I did download the file it generates and tried to, but again it could not read it due to the size.
Ideally if you could break the it into multiple feeds it would work better with our product.
Let me know if you have any follow up questions.
Thanks