@CraigCoulter Just noticed that you have gone through that same issue like I did. The spindle works but the speed goes straight to 24000RPM via RS483. In case anyone else stumbles upon the same issue. The missing bit is to change PD144 on your VFD to match the RPM of the spindle at 50HZ. The default is set to 1440. In my case, setting it to 3000 fixed the issue and everything now works correctly.
Hope this helps.
This probably is worth mentioning in the spindle documentation.