Error code is 0xc004f050 and the message (translated from German is "The entered product key does not work...")
OK - that Pro License has an issue, has it been used previously? Is it a Multiple Activation Code or Volume License Key?
Here is the troubleshooting site from MS: https://support.microsoft.com/en-us/help/10738/windows-10-get-help-with-activation-errors
On the MS forums this error usually resolves itself, but I would reach out to MS Support.