Missing PHPMailer is Required for SMTP to function

For anyone has this problem with version 8.x-1.2 after you use composer add package "phpmailer/phpmailer", just add a "\" before namespace "Drupal\smtp\Form\SMTPConfigForm" line 5 of file "smtp.info.yml", the problem is caused by the missing of root namespace.

@swatchion you probaly mean on the file `smtp.routing.yml`

I stumbled into that issue also.
Having installed modules via `composer require drupal/smtp` and `composer require phpmailer/phpmailer`, I still got that error message.

After a bit of search, I noticed that the permissions for my phpmailer folder were wrong (no webserver permissions).

Anyway, after I changed the permissions with `chmod -R apache:apache vendor/phpmailer`, I still got the error message, but basically it should work at this step.
Rebooting php and httpd finally got rid of the error message.

I can´t depend on Composer as I don´t have VPS.
Why can´t I download that library and upload to lib's folder as usually?