I have installed Best Answer before.
It was working perfectly fine in beta14.
But in beta15, it won't install.

I use

composer require fof/best-answer: "*"

It installs fine. But it can't open flarum

It prompts an error

Flarum encountered a boot error (Error)
Call to undefined method Illuminate\Support\Reflector::isCallable()
thrown in /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php on line 691
Error: Call to undefined method Illuminate\Support\Reflector::isCallable() in /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php:691
Stack trace:
#0 /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php(653): Illuminate\Console\Scheduling\Event->skip()
#1 /www/wwwroot/wyz.xyz/vendor/fof/best-answer/src/Console/NotifySchedule.php(27): Illuminate\Console\Scheduling\Event->withoutOverlapping()
#2 /www/wwwroot/wyz.xyz/vendor/fof/console/src/Extend/ScheduleCommand.php(29): FoF\BestAnswer\Console\NotifySchedule->__invoke()
#3 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/Extension.php(137): FoF\Console\Extend\ScheduleCommand->extend()
#4 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/ExtensionManager.php(334): Flarum\Extension\Extension->extend()
#5 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/ExtensionServiceProvider.php(30): Flarum\Extension\ExtensionManager->extend()
#6 [internal function]: Flarum\Extension\ExtensionServiceProvider->Flarum\Extension\{closure}()
#7 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Foundation/Application.php(322): call_user_func()
#8 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Foundation/Application.php(263): Flarum\Foundation\Application->fireAppCallbacks()
#9 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Foundation/InstalledSite.php(148): Flarum\Foundation\Application->boot()
#10 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Foundation/InstalledSite.php(81): Flarum\Foundation\InstalledSite->bootLaravel()
#11 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Http/Server.php(56): Flarum\Foundation\InstalledSite->bootApp()
#12 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Http/Server.php(33): Flarum\Http\Server->safelyBootAndGetHandler()
#13 /www/wwwroot/wyz.xyz/public/index.php(22): Flarum\Http\Server->listen()
#14 {main}

I also can't execute

php flarum cache:clear

[root@iZhp323kivrtzzrhxikp2aZ wyz.xyz]# php flarum cache:clear
PHP Fatal error:  Uncaught Error: Call to undefined method Illuminate\Support\Reflector::isCallable() in /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php:691
Stack trace:
#0 /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php(653): Illuminate\Console\Scheduling\Event->skip(Object(Closure))
#1 /www/wwwroot/wyz.xyz/vendor/fof/best-answer/src/Console/NotifySchedule.php(27): Illuminate\Console\Scheduling\Event->withoutOverlapping()
#2 /www/wwwroot/wyz.xyz/vendor/fof/console/src/Extend/ScheduleCommand.php(29): FoF\BestAnswer\Console\NotifySchedule->__invoke(Object(FoF\Console\Overrides\CustomSchedule))
#3 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/Extension.php(137): FoF\Console\Extend\ScheduleCommand->extend(Object(Illuminate\Container\Container), Object(Flarum\Extension\Extension))
#4 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/ExtensionManager.php(334): Flarum\Extension\Extension->extend(Object(Illuminate\Container\Container))
#5 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/ in /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php on line 691

Fatal error: Uncaught Error: Call to undefined method Illuminate\Support\Reflector::isCallable() in /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php:691
Stack trace:
#0 /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php(653): Illuminate\Console\Scheduling\Event->skip(Object(Closure))
#1 /www/wwwroot/wyz.xyz/vendor/fof/best-answer/src/Console/NotifySchedule.php(27): Illuminate\Console\Scheduling\Event->withoutOverlapping()
#2 /www/wwwroot/wyz.xyz/vendor/fof/console/src/Extend/ScheduleCommand.php(29): FoF\BestAnswer\Console\NotifySchedule->__invoke(Object(FoF\Console\Overrides\CustomSchedule))
#3 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/Extension.php(137): FoF\Console\Extend\ScheduleCommand->extend(Object(Illuminate\Container\Container), Object(Flarum\Extension\Extension))
#4 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/Extension/ExtensionManager.php(334): Flarum\Extension\Extension->extend(Object(Illuminate\Container\Container))
#5 /www/wwwroot/wyz.xyz/vendor/flarum/core/src/ in /www/wwwroot/wyz.xyz/vendor/illuminate/console/Scheduling/Event.php on line 691

If you uninstall best-answer
flarum can be restored to normal