Hi,
1. The access of the plugin should be public. The cron URL is automatically triggered by our server. If you set it to something else than public, the plugin will never run when our server triggers your cron URL.
It doesn't change anything for security.
Sure, anyone could access your cron URL but the cron will only run based on the frequency you configured in its settings (and same for the plugin), so even if someon tries to call it many times every second, it just won't do anything.
2. The error I see when the cron is triggered is:
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And
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is the root of your website. So what you write is that field must be relative to the root of your website. Your CSV file must be somewhere else.
I tried to check where the file it with the FTP access, but it only leads to a folder where there is only that CSV file, so it doesn't help at all.
Here, I would actually recommend to put the CSV outside of the website directory and enter the absolute path of the CSV file on the server. That way, no one would be able to access the data of your CSV (if you're worried about that, security-wise).