NSURLErrorDomain fout -999. when activating icloud photo

Hello there,

Since a long time my cloud photo library doesn't synchronize on my MacBook. I do want to have the photo's from my iPhone and other devices on my MacBook.

In trying to solve this problem I unclicked the button saying "iCloud Photo's" in the photo library. After an update and 2x restart the button still cannot be clicked "on". I get two pop-up screens over one another saying "You can't control your memory at this moment. Please try again later." and over this pop-up comes the one with "your command cannot be performed (NSURLErrorDomain fout -999.)"

How do I get my iCloud photo library into my photos app on my MacBook?