Hi GillesDM,
This is the default response from InfinityFree hosting servers for requests without the security cookie headers, a JavaScript anti-bot measure to be precise. As far as free hosting is concerned, automated bot access is not allowed/recommended/whatever.
You maybe able to get around this by using a custom domain on your website, alternatively, use email method instead if you need reliable automation. As you have Fastcron access, you can have that job to access a certain mailbox and resolve your data from there.
As for your website, you can call SMTP providers’ API to send an email to yourself and have them stacked there until a cron is executed.
If you’re dealing with business critical mission here, just upgrade instead.
If you wish to know more, a technical discussion can be found in Informal:
Cheers!