Sorry to hear of the problem you are having.
It seems you are having server related issue so please make sure you have configured your site SSL correctly or contact your webhost.
Alternatively you can install extensions manually as described in the following page.
Would you mind if i log in to your site and do some troubleshooting? If this is ok then could you please share me your site log in details privately by adding them in the box having text “Click here to share private content. Only you and forum moderators will be able see it.”?
Also have you contacted your web host to resolve the cURL error?
Please make sure you are using latest version of PHP on your server by referring the information provided in the following page.