The software is Sound Forge 12.6 (for years I have been using previous releases with success) - I was given a registration number that is "refused" - They are quick for receiving payment but terrible for direct support and practical intervention, and there is nothing "magic" about their website. Sad, sad, very sad...
Welcome to the Magix Sound Forge users community @Francis-Montagnier.
I was given a registration number
Who gave you the activation number? The activation serial code alone will not activate Magix versions of Sound Forge. If it was previously registered and activated, you must use the email address that was used then. The activation code and email are paired. One license allows SF to be activated on (2) PCs simultaneously. Log-in to "Magix Customer Service> My Products" to see the activation info. See this recent comment about deactivating and reactivating.
They are quick for receiving payment
Who are "they" ? If it was purchased recently, it was not from Magix. The current Sound Forge version number is 16. SF-17 will be published in the not-to-distance future
@Francis-Montagnier If you try to use a voucher code a second time, this isn't possible. You either need to re-download the software from your user account. Or, if installed the software from the Music Maker in-app-store, you need to re-download it from there.