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 exist some events, relative to current or future days.
You can download this .ics feed and open in notepad and check your events there.

2) If events was imported before, then such events will not be imported again.
Booking Calendar can import the events from external sources only once (if have not been activated options "Force import" or "Trash all imported bookings before new import" at the Booking > Settings > Sync > "General" page in Advanced section).

May be you are having these event(s) in the Trash or such event(s) was imported into not exist booking resource.

In this case, you need to delete such previously imported bookings (that was imported into non exist booking resource), and then try to import these bookings once again by using correct shortcode.

3) How to check if events, was imported before into Booking Calendar?
3.1) Please update the Booking Manager plugin to the latest update.
3.2) This point work only in Booking Manager 2.0.11 or newer versions.
Open the "oPlugins Panel" > Settings > "Listing Template", and define in listing template these shortcodes:

<p>UID: [UID] ( Booking ID: <a href="[BOOKING_LINK]" target="_blank">[BOOKING_ID]</a>  )</p>

3.3) Open "oPlugins Panel" > "Manage .ics" page, then paste URL of your .ics feed (that you need to check), and click on "Show Events (.ics)" button.
You will see all the events from this .ics feed. Also in each event you will see ID of booking, if its was imported, like this:

Booking ID: 101
if the booking was not imported you will see this:
Booking ID:

You can click on booking ID link to open the Booking Listing page with this specific booking and see, details of this booking. Check the booking resource, where this booking saved.

4) If the booking was not imported, then please recheck parameters of import shortcode.
Please check carefully parameters, like:
import_conditions - if you defined import_conditions='if_dates_free', then event will be imported only, if the source booking resource (calendar), have all dates for this event as available
from - date from which start to import events. Usual value: from='today'
until - date of stop import events. Usual value: until='any'

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