I am having an issue importing ics feed from external source.

If you do not see imported bookings, from external .ics feed, then please recheck these points:
1) Please be sure that in your.ics feed was some events, relative to current or future days. You can try to download this .ics feed and open in notepad and check your events there.

2) This issue can be because of these events was imported before.
And may be you are having these event in the Trash or such events was imported into not exist booking resource.

Booking Calendar can import the bookings from external sources only once.

You need to delete previously imported bookings (that can imported into non exist booking resource, and you have some lost bookings), and then try to import these bookings once again by using correct shortcode.

How completely delete bookings from the Booking Calendar?

1) You can erase bookings from the Booking Listing page.

Please open the booking listing page, then open the link like this: ( description about it here: https://wpbookingcalendar.com/faq/lost-bookings/ )

https://server.com/wp-admin/admin.php?page=wpbc&wh_booking_datenext=1&wh_booking_dateprior=1&wh_booking_date=3&wh_trash=any&wh_modification_dateprior=1&wh_modification_date=3&wh_pay_status=all&view_mode=vm_listing&wh_booking_type

of course https://server.com you need to replace to your website DNS.

Its will show all your exist bookings.

2) Select your bookings, by setting checked checkbox at the left side near each booking.

3) Switch to the Actions toolbar and then click on the Delete button (not the trash). Its will completely delete selected bookings, without moving them into the trash.
Also its delete selected bookings, even if such bookings currently in the trash.

So by doing these steps you can erase all bookings, completely.

After this try to import new bookings once again.

Check this instruction how to start import of new events/bookings.