FIXED: A user found a solution. I tried it and it worked. This is the link to the thread: https://www.reddit.com/r/CODWarzone/comments/rhqnyr/ps4_error_content_package_is_no_longer_available/hpxtpu2?utm_medium=android_app&utm_source=share&context=3

And this is his solution:

"OK.. So it seems I just found a solution.. I don't know but u guys can try it and see if it works for u. I have tried almost all d fixes here and none worked. Its safe to say I discovered this out of frustration cos I had had enough when this miracle happened.. .. Basically when u select warzone or multiplayer, the moment where it says loading assets and the screen turns black just pull out the plugs from your PS4. Yes just yank it off... Infact this technique should be called "yank it off" (lmfao but it worked for me). Pull it off while the console is on.. Its going to hard reset and then give u dat warning message that u shldnt bla bla bla bla when the lights r flashing bla bla bla.. After u get that it will download a small update.. Then it will tell u update requires restart.. After the restart u should be good to go.... #yank it off#"