Installing Nextcloud on Macbook

Hello, I managed to installed Nextcloud on my MacBook Pro. But I cannot seem to synchronise my files. I always get a little red x when I try to synchronise files from my end. Any help ?

Can you open the Nextcloud client, then you should be able to get a bit more details on why there is the red cross. If there isn’t any more information, with F12, you can open a logging windows.