Please visit the download page where you can find builds for all our products and their supported versions.
Select your product and then select the version you wish to use (should be the same as the product you have installed on your machine) . Click on the "Download" button and run the installer.
In order to see older versions, check the “Show all versions” box in the right corner of the downloads section.
For example if you are using Maya version 2019 you need to download a build for V-Ray for Maya version 2019 as otherwise your license will not start properly.