Just found this which solved it for me:
https://github.com/laravel/reverb/pull/85
Specifically this bit - updating the reverb.php to include this:
'options' => [
'tls' => [
'verify_peer' => false,
],
],
Finally, ensuring that the reverb_host is the domain, the reverb_scheme is https, and the reverb_port is 8080.
Once all that was in place, running npm run build (or npm run dev) then restarting the reverb instance (php artisan reverb:start) had it working for me.