The error code you mentioned is coming from your VPN - possibly not even the VPN connection can be established properly.
Some points I would mention to check:
1. You mentioned that you set your router's IP as the address of your VPN connection. This means, that your laptop can connect to the router, but still can't find the server machine.
In this case, you must set port forwarding, so the VPN connection can found the proper machine behind the address. This is strongly depending on the devices and software you use, so I would suggest to ask for help from someone who is familiar with it, or try to search for the products for further instructions.
2. Using a dynamic IP for BIMcloud Basic is possible, however, we really don't recommend to do that.
The reason is that both the components of the BIMcloud, and ARCHICAD are constantly using the address to communicate with each other. In case your IP is changed, these components and ARCHICAD clients can no longer connect.
3. Using a free option, such as noip.com is a possible solution, but don't forget that these free licensed programs has some limitations, which can cause further trouble (see my second point).