"Preparing" and refuses to send

I was able to test send the campaign. ie. "Email has been sent!". And able to received the email.

However, when tried to "Send newsletter now", Campaigns says "Preparing" and refuses to send.

I've reset and added the cron. Web host confirmed cron is running every 5 min.

Sendy Version 6.0.9
Tried php 8.0, 8.1 and 8.2

Here is the log:
[27-Jan-2024 08:30:03 Asia/Kuala_Lumpur] PHP Warning: Undefined array key "SCRIPT_FILENAME" in /home/xxxx/public_html/scheduled.php on line 693

Could be the error?
//Get server path
$server_path_array = explode('scheduled.php', $_SERVER['SCRIPT_FILENAME']);
$server_path = $server_path_array[0];