I've just purchased "Video deluxe Plus 2020" from a Swiss dealer. I have the license key, but I can't use that to do the download, which apparently requires a voucher.
"Video Deluxe Plus 2020" is actually known, in English, as "Movie Edit Pro Plus" so I have changed your product details for your post.
Under normal circumstances I would suggest to you going to this product page to download the Free Trial version of MEP Plus and then using your supplied licence key to fully activate it. However, the latest version is actually "MEP 2021" so your licence/serial key is not going to be valid, I think? On the other hand, purchase of the software/serial key does also access the "12 months Update Service" so I wonder whether you can, in fact, download and install the new version and then register it with your supplied key?
To be safe, I suggest you use this page to send a message to Magix Sales and ask them whether you can, in fact, download the latest version and install it with the key you have already bought.
One final thought: perhaps you should ask the dealer from whom you bought the key to also supply you with a download link.
If you have a legitimate licence key you can use it in a trial version to fully activate it. Whether you get the additional third party effects on offer I can't say.
[Edit] Just seen your post Jeff. Yes good points to consider.
Apparently someone has done something, because this time when I plugged in the license key where the voucher is required, everything worked. I received an email with one serial number and download links for both Video Deluxe Plus and Movie Edit Pro Plus. I'm not the end user (building a system for a friend), so I'm a bit mystified as to what the difference is between the two programs that I just downloaded.