If you are testing SightCall in Chrome and are getting a message to download the plugin despite your previous installation of both the plugin and the extension, the following steps could help:
1. Check that you are able to connect to console.sigthcall.com using Internet Explorer
2. Check the chrome policy (chrome://policy) in Chrome
3. Check that you do not have anything in "NativeMessagingBlacklist"
4. Add (or ask your IT to add) the following value to NativeMessagingWitelist: com.sightcall.chrome.driver