Need help installing WP Smush Pro; and regular Smush is not working

I purchased the free trial of WP Smush Pro and downloaded it, but it's not showing up in my plugins, Only the free version. So I decided to you ahead and use the free version. But the free version is not working either. Here's the error message I received:
Error posting to API: cURL error 6: Could not resolve host: smushpro.wpmudev.org (Timeout while contacting DNS servers)
Error posting to API: cURL error 6: Could not resolve host: smushpro.wpmudev.org (Could not contact DNS servers)
Error posting to API: cURL error 6: Could not resolve host: smushpro.wpmudev.org (Timeout while contacting DNS servers)
Smush request timed out, You can try setting a higher value for WP_SMUSH_API_TIMEOUT.