Books won't sync through devices

Hi all,

I've been experiencing problems with the Books app across my devices. I own a MacBook Pro (13", Mid 2014) with the latest Catalina (10.15.4) running it, and an iPhone 7 with the latest iOs 13.4.1 running it.

The problem:

1. Books on my Mac doesn't sync with the one one my iPhone. Both on my Mac and my iPhone Books is synced with iCloud.

2. I can't access the book stores on Books on my Mac, nor won't it update existing files (see screenshot)

Does anyone know how this can be sorted?

Thanks a billion in advance!

Greets,

Caia