First, can you tell us where, exactly, you bought Photo Manager? If it was direct from Magix you should have received an email with a link to download the software and a serial key, not a voucher code, which you enter on the Registration screen once the software is installed and you try to run it for the first time. This serial number may not be immediately obvious in that email; you may need to ensure you read right to the end of it.
If you bought the software from a third-party seller then you should have received a voucher code, either in any box you were given or in a confirmation email. If you did not receive such a code you need to ask the seller to supply it as a matter of urgency. Magix will have no record of your purchase and so cannot directly help you, sorry.
Just for clarification: full instruction on how to redeem a voucher code are found on this page.