Cannot activate FreePBX 16 at home

I’m trying to use FreePBX 16 at my house. I’m using a cable modem, router with Tomato, NGINX reverse proxy to host various websites, and FreePBX is running on a computer running VirtualBox. I let it do the automatic network config but now when I reach the Activation screen → Create Portal Account → [Create] button does nothing. There’s no apparent error message.

What am I doing wrong?