@AndyMatthews 

Hi, 
You can refer to the instructions below to troubleshoot if you fail to establish the RTSP/Onvif connection.
What can I do if fail to stream the Tapo camera via the RTSP/ONVIF protocol?
 

If the problem remains, please confirm the following information.
1. The network diagram. Are the camera and computer installed with the VLC connected to the same Wi-Fi network? Can you ping the camera's IP address successfully on the computer?
2. What URL have you used on your VLC when streaming the camera?
3. Please send us a picture of the error message when trying to establish the RTSP/Onvif connection.

Best Regards

  @AndyMatthews 

Hi,
Usually, the RTSP/Onvif connection has no special requirements about the format of the camera account. Your problem is more likely related to the third-party app/program and the setup process.
What app/program you are using to connect to the camera via RTSP? Would you please send us a video showing the whole setup process? Please describe your network diagram to check if your setup process is correct.
Best Regards