Error 408 is displayed when a subscription plan activation is attempted with an older version of RadiAnt (e.g., 4.6 or 5.5). You can check the version of your viewer on the title bar of the activation window.

RadiAnt DICOM Viewer 2020.2 (or newer) is required to activate the subscription plan successfully. Make sure that you have the latest version installed. You will not be able to activate the plan using older versions of the software.

Please download and install the latest version from: https://www.radiantviewer.com/download/.