How do I use my beta key for the Call of Duty Modern Warfare beta?

I have today bought a beta key on MMOGA, unfortunately there's no guidance where exactly I have to redeem the code and I think nothing. At least it is not possible on the playstore. So I want to play the beta on Ps4.

The https://de.mmoga.net/Game-Keys/Call-of-Duty-Modern-Warfare-2019-Closed-Beta-Key-PC-PS4-Xbox-One.html product page says, "You can simply activate the key on the manufacturer's website to download the game." No idea how it works with the PS4.

Yes, but I know exactly that is the problem I do not want to redeem the one at once and then I have it on pc

And what exactly leads you to believe that you get a PC version with a license key for the PS4? The keys are different.

This is not a key for ps4, this is a key for ps4 / xbox and pc that's why I'm unsure

As a non-Konsolero I hold myself better out of it.