PHPmailer dependency loaded from the wrong location.

Yes, this change will fix the issue ../vendor/phpmailer/phpmailer/src/SMTP.phpbut this path we need to fix like in my case the path is

require_once 'vendor/phpmailer/phpmailer/src/SMTP.php';

notice the "../" part in the fix.

Tried sending the email by making this change and it worked.

Seems like this was fixed in commit be510aa5a3adaffe462417cdc61975fdb4c299c8, which was included in v4.0.1

It is not fixed yet, we are still getting the error and this code needs refactoring otherwise hardcoded path could create issues and additionally could be included by using namespaces.