Can't log into App Store (MacBook Pro 2018, Mojave 10.14.3)

Hey There,

I have a newly bought MacBook Pro (15-inch, 2018) using Mojave version 10.14.3 (18D109).

When I try signing into App store from the OS, the window disappears like the password is approved and I'm signed in, but I'm not and it still says sign in, in the bottom left corner.

If I put in a wrong password it stops me so it is obvious the password is checked but still I don't get signed in and can't use the app store.

I have an iMac as well with the same OS, but late 2015 model, and I can sign in there using the same credentials without any hassle.

Have tried resetting certificates, and of course my computer as well and password.

Please advice.