This error message means that your PHP installation is partly broken.
Specifically, it has missing or out-of-date SSL certificates. Up-to-date ones are needed to verify that your connection to the remote site (e.g. Amazon S3, DropBox, Google) is secure.
Your web hosting company should fix this (or whoever is operating your web server). It should not cost you anything: it is something broken.
If your web hosting company refuses to fix it, then we recommend Simba Hosting, who will transfer your existing website for no additional cost.
There really is NOTHING that can be changed inside UpdraftPlus to take away the above error: either your web server needs fixing, or it needs changing.