Admin Ajax Error 500

Bookly works fine when I’m logged into wordpress. But when customers view it they get the endless loading spinner.

This error is in devtools:
Failed to load resource: the server responded with a status of 500 ()
wp-admin/admin-ajax.php?action=bookly_render_time&csrf_token=8ba999b011&form_id=5f9b8b295addc&new_chain=true

Here’s the debug log:

[30-Oct-2020 03:33:43 UTC] PHP Notice:  Trying to access array offset on value of type null in /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/frontend/modules/booking/Ajax.php on line 1167
[30-Oct-2020 03:33:43 UTC] PHP Notice:  Trying to access array offset on value of type null in /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/frontend/modules/booking/Ajax.php on line 1168
[30-Oct-2020 03:33:43 UTC] PHP Notice:  Trying to access array offset on value of type null in /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/frontend/modules/booking/Ajax.php on line 1169
[30-Oct-2020 03:33:43 UTC] PHP Notice:  Trying to access array offset on value of type null in /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/frontend/modules/booking/Ajax.php on line 1195
[30-Oct-2020 03:33:43 UTC] PHP Fatal error:  Uncaught Error: Call to a member function withSubServices() on bool in /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/lib/slots/Finder.php:411
Stack trace:
#0 /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/lib/slots/Finder.php(106): Bookly\Lib\Slots\Finder->_prepareStaffData()
#1 /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/frontend/modules/booking/Ajax.php(208): Bookly\Lib\Slots\Finder->prepare()
#2 [internal function]: Bookly\Frontend\Modules\Booking\Ajax::renderTime()
#3 /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/lib/base/Ajax.php(52): call_user_func(Array)
#4 /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/lib/base/Ajax.php(31): Bookly\Lib\Base\Ajax::forward('renderTime', true, true)
#5 /nas/content/live/thedirt4wd/wp-includes/class-wp-hook.php(287): Bookly\Lib\Base\Ajax::Bookly\Lib\B in /nas/content/live/thedirt4wd/wp-content/plugins/bookly-responsive-appointment-booking-tool/lib/slots/Finder.php on line 411

The page I need help with: [log in to see the link]