Being an Australian firm, occasionally there are financial glitches between countries. Get in touch with NCH They will make it right.
https://www.nch.com.au/support/reg.html
Be sure that you registered VP via the Menu at the top-left. A box will drop down with a Registration link at the bottom. Follow the instructions to obtain your code. Upgrades are free for a six-month period, but if your version is doing well stick with it. You can always test drive the latest release, to check out new features or better performance. Retain your registration code and original installer.
If mp4 export isn't available, try AVI. That may get you going until the app is properly registered. You can also try out the very latest version.
When editing, Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite.