3rd Party Cookies
Hiver is a browser-based extension for Gmail for which you should have your Content Settings configured to Allow Third Party Cookies.
Find the following link to find the option to Allow Third Party Cookies
Alternatively, you can follow the given steps to navigate to that option
1. Click on the three perpendicular dots on the top right of your browser to see the options
2. Click on Settings
3. Scroll down the page to locate 'Advanced' and click on it to see the options
4. Click on 'Content Settings' to see the options
5. Click on 'Cookies' to see the options
6. Disable 'Block third-party cookies'