Check Queue Worker: Since the export process is likely queued,

ensure that your queue worker is running. 

If you're using Laravel's queue worker, 

you can start it with the following command:

php artisan queue:work

If the queue worker is not running, 

the export will be processed but the notification might not be sent.

for more information visit this link , it will help you solving :

https://laracasts.com/discuss/channels/filament/filament-exporter-action-not-showing-notification-when-export-is-complete

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