SOLUTION: For those of you struggling with the problem of Booking.com saying that the Airbnb iCal link is NOT A VALID ICAL URL, I have a solution..
I had the same problem. I selected the iCal link from Airbnb and pasted into Booking.com, and I got this error.
It turns out that when you select the contents of the dialog box that contains the iCal URL on the Airbnb site, you're only selecting the visible text.There is however additional text to the right that you can't see and which isn't selected. This means you're only copying part of the URL. To select the full URL you have to click in the box and then drag the cursor to the right, which will reveal the rest of the link. You can then select all of it by clicking and dragging all the way to the left.
If you select, copy and paste the full URL into Booking.com, it works right away. Yay!
SOLUTION: For those of you struggling with the problem of Booking.com saying that the Airbnb iCal link is NOT A VALID ICAL URL, I have a solution..
I had the same problem. I selected the iCal link from Airbnb and pasted into Booking.com, and I got this error.
It turns out that when you select the contents of the dialog box that contains the iCal URL on the Airbnb site, you're only selecting the visible text. There is however additional text to the right that you can't see and which isn't selected. This means you're only copying part of the URL. To select the full URL you have to click in the box and then drag the cursor to the right, which will reveal the rest of the link. You can then select all of it by clicking and dragging all the way to the left.
If you select, copy and paste the full URL into Booking.com, it works right away. Yay!
:)