A little bit of background here. I previously had High Sierra installed on my Macbook Air, but for some reason, at one point when I tried to boot up my mac, it showed a folder with a question mark sign that kept flashing. Luckily for me, I was about to upgrade to macOS Mojave, so I had a bootable disk with Mojave on it. I created a new volume on the existing Container in recovery mode, installed Mojave on it and copied out files from the corrupted High Sierra Volume.
Now, I had previously read on some articles and forums that the way to move keychains manually to a new mac was to navigate to ~/Library/Keychains/ and copy out the login keychain, but I found out that Wifi passwords were stored on the System keychain in Keychain Access, so I navigated to /Library/Keychains/ and copied out System.keychain along with the login keychain from the user folder and I deleted the volume.
Coming to my Mojave and opening up the High Sierra's System.keychain in Keychain access, I found that I was unable to copy the Airport passwords to my main Mojave System keychain because it was requesting for the High Sierra's System.keychain password. This is puzzling, because I already was able to unlock the High Sierra's System.keychain with my Mojave user password which by the way is the same as my previous High Sierra user password.
Typing in the correct password doesn't work, the pop up window just jiggles to show that the password is incorrect. I don't know what else to do, as I have quite a lot of Wifi passwords. Please, any help would be appreciated.