With the release of Akeeba Backup 7 there are some changes in the support of remote backup generation.
Free Version of Akeeba Backup 7 is Not Supported by YourSites
The developers of Akeeba Backup have removed the ability to generate and access backups remotely from non-Professional versions of Akeeba Backup. You will therefore need to install Akeeba Backup Professional on your client sites in order to generate and check your site backups from YourSites.
The developers had not anticipated that this functionality would be used in the free releases of Akeeba. I quote:
Over the years some Professional features had accidentally ended up in the Core version -- the accidental nature of the transition is why they were still listed as Pro-only in our product pages. This made sense neither for us nor the target audience of the Core version of the software. Giving less reason to users who can plausibly afford a subscription to buy one has had a negative effect both on the sustainability of the project as well as our ability to contribute back to the Joomla and WordPress community, either financially (sponsorships) or with our personal time. We hate freeloading off the community; it's unethical.
You can read more about these changes here https://www.akeebabackup.com/news/1726-akeeba-backup-7.html