Hi Guillermo,
So virtualbox did throw an error on my mac running Mojave, but it worked without problem's on two of my colleague's macs (one running Sierra, the other also running Mojave) so that appears to be an error on my end.
I was following this guide (https://docs.opendatakit.org/aggregate-vm/), that under "Connecting to the VM from external apps" indeed states that I should run the aggregate-config command. However, first in step 3 the VM should give me an IP address, that then feeds into the aggregate-config command. The IP address never changes on my end, it remains stuck at http://localhost:10080.