This error can happen for two reasons. The first is that there was an error when entering the license key. If the whole license key wasn’t copied and pasted into the License Key input, it won’t be considered a valid key and will cause the error.
The other reason this error happens is that you have recently upgraded your subscription of Link Whisper, but haven’t updated the version of Link Whisper on your site.
When you upgrade your subscription, you need to delete the copies of Link Whisper from your sites and replace them with new copies downloaded from linkwhisper.com. This is because the version installed on your site is specific to your license level. So when you upgrade your license, your license key won’t work with the installed copies of Link Whisper.
To fix this, you need to first deactivate and delete the copies of Link Whisper from your sites. Then download and install new copies from linkwhisper.com. Installing new copies of Link Whisper won’t change or delete your settings.