Adrian, I think the issue is PIPCost. As per Zorro Docs:
> PIPCost - ... For calculating it manually, multiply LotAmount with PIP; ....
https://manual.zorro-project.com/pip.htm


I stumbled across the same issues trying to purchase fractional crypto and managed to fixed it by playing with the PIPCost.

In my case, I assumed the PIPCost was correct as it was generated by the Coinbase public plugin. I created an an issue on that repo where I also outlined my discovery process: https://github.com/kzhdev/gdax_zorro_plugin/issues/1