Cannot Send Emails

My Mautic version is: 4.15.0
My PHP version is: 7.4.16
My Database type and version is: ?

Your problem
My problem is: Cannot Send Emails

These errors are showing in the log:

[2021-04-27 00:20:07] mautic.NOTICE: Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: The “swiftmailer.transport.real” service or alias has been removed or inlined when the container was compiled. You should either make it public, or stop using the container directly and use dependency injection instead. (uncaught exception) at /var/www/html/mautic/vendor/symfony/dependency-injection/Container.php line 275 while running console command mautic:emails:send

[2021-04-27 00:20:07] mautic.WARNING: Command mautic:emails:send exited with status code 1

Steps I have tried to fix the problem:

Someone gave me this solution, but I am not sure what they mean. Do I make this change somewhere in WINSCP, Putty, mautic, etc? Can someone please help me with this work-around?

"found a workaround:

replace it with:

/var/www/html/mautic/bin/console swiftmailer:spool:send --message-limit=1 --env=prod

the above limit=1 can be changed to anything u want"