A note for anyone who finds themself here: This may be due to my inexperience with Docker perhaps but I had issues getting this working. The issue is 100% on the side of my network somewhere, but for some reason I'm not able to get this to connect to my Roundcube instance if it's sending a request to $mailcow_hostname. I am using Mailcow on a VM under Proxmox and was only able to resolve my issue by replacing the mailcow hostname with the IP address of the VM it's running on. If anyone has any idea how to fix this 'the right way' let me know, but this is how I dealt with the error 'Unable to get token, is your RC link correct?', as requests to the hostname were timing out.

I have the same issue "'Unable to get token, is your RC link correct?' However I didn't figure out where exactly to replace the $mailcow_hostname with the ip address. Mailcow is running on a linux surver in a docker stack, roundcube is also running in a different docker container.