Hi @vanvaldenburg!
Please make sure you read the instructions thoroughly and followed them correctly.
If so, let's narrow down the possible error causes.
Is the RTMP URL correct? Did you successfully stream to it before, without the nginx layer between?
If yes, the problem could be in the nginx configuration.
Is there an error.log existing in the logs subfolder of nginx (e.g. C:\Program Files (x86)\nginx-rtmp-win32-master\logs)?
This usually gives a pretty good idea about the problem's cause.
Please let me know if you made any progress or if there is anything you need help with.