Image smush failed: "error 77: Problem with the SSL CA cert"

I have installed WP smush to make my images smaller. But they get an error for more than half of my images (about 500) and cannot make them smaller.
The error is:
"Error posting to API: cURL error 77: Problem with the SSL CA cert (path? access rights?)".
I use a plugin called Really Simple SSL to make my site https.
I contacted hostgator about this issue and they said "your ssl is installed and is working correctly." They said I have to contact the plugin developer.
Thanks for your assistance.