How to add encryption key before mounting my external .pak using C++

I need to decrypt my own external .pak in Unreal Engine 5.6 in order to load its content.
I need to store my encryption key in C++ code, not in the project settings.

How can I add the encryption key before I mount it using C++ ?

I have tried this code Under UE 5.4 and it works:

UE::FEncryptionKeyManager::Get().AddKey(FGuid(), GetEncryptionKey());

But under UE 5.6 the header is not accessible anymore.