@AlexT Neither of your examples are correct. You have to use the file system paths on the web server for php and also the config file. If you don’t know what they are then you will need to ask your hosting company.
You now do not need to run the autoresponder process page, but do need to run the phplist process queue page regularly. Upgrade the autoresponder plugin to get the new functionality.
Possibly your hosting account might not provide the cron job support that phplist needs.
It is not possible for the autoresponder to be sent immediately after a new subscription. The campaign will be sent on the next run of process queue, so you need to decide how long an interval you want, and that will influence the frequency of running process queue.